This is a translation of a Q&A posed to Shaykh Hobbollah, original Arabic here
Question: Some infer the authenticity of a narration on Arbaʿīn and other narrations regarding the matter of visiting Imām al-Ḥusayn – peace be upon him – on the fortieth, by saying: these narrations are famous among the jurists, even the later ones. How true is that?
I could not find anything related to Zīyārat al-Arbaʿīn except for the following:
The first narration: What was narrated on the authority of Abī Muḥammad Al-ʿAskarī (peace be upon him), that he said:
The signs of the believer are five: prayer of fifty (rak’at), Zīyārat al-Arbaʿīn, wearing a ring on the right, soiling of the forehead in prostration and pronouncing Bismillah hir Rahman nir Raheem loudly
And this narration was mentioned in Miṣbāḥ al-Mutahajjid (788) by Shaykh al-Ṭūsī and also in his Tahdhīb al-Aḥkām (6/52), and this is the oldest source for it  and it is a mursal  narration, rather there is no chain of transmitters mentioned whatsoever; because Shaykh al-Ṭūsī said: “It has been narrated”, and there is approximately 200 years between Shaykh al-Ṭūsī who passed away in the year 460 AH and Imām al-ʿAskarī (peace be upon him) who passed away in the year 255 AH, so the narration is not reliable by its chain. And there is nobody from the researching scholars in the science of Rijāl and Ḥadīth that considers the disconnected narrations of Shaykh al-Ṭūsī authentic.
And this narration is also mentioned by al-Mashhadī in Kitāb al-Mazār (352) while saying: “And by the chain on the authority of Abī Hāshim al-Jaʿfarī, on the authority of Abī al-Ḥasan al-ʿAskarī […]” and al-Mashhadī himself is not established as trustworthy according to scholars like Sayed al-Khoeī, and we don’t know his chain to al-Jaʿfarī either.
The second narration: The report of Ṣafwān al-Jammāl on the authority of Imām al-Ṣādiq (peace be upon him) saying:
My mawla Imām al-Ṣādiq (peace be upon him) said: “During Zīyārat al-Arbaʿīn visit in the rising of the day, and say: Peace be upon you O Friend of Allah and his loved one […]
See: Tafṣīl wasāʾil al-Shīʿa (14/479-87).
And this narration is more clear as evidence compared to the first narration, because the first narration does not elaborate on what is meant by al-Arbaʿīn in the report, is it forty believers or something else? And if some argue that what was meant was forty believers then it would’ve been said as: Zīyārat Arbaʿīn and not: Zīyārat al-Arbaʿīn. While the second narration is not like that at all [in terms of lack of explaining the meaning of Zīyārat al-Arbaʿīn], the second narration is also weak by its chain; because in it there is Muḥammad b. ʿAlī b. Muʿammar.
Some have attempted to authenticate him because he is from the mashāyikh  of al-Kulaynī and this does not establish trustworthiness.
Or they attempt his authentication by saying Ibn al-Nadīm counted him from among the group of Shiʿā jurists and scholars he spoke about, see Fihrist Ibn al-Nadīm (278). And this is no evidence; because the praise of ones knowledge does not suffice for their authentication. How did Ibn al-Nadīm include Sahl b. Ziyād al-Ādami, whose weakness was explicitly stated in the words of more than one of the classical Imāmī scholars, and Ibn al-Nadīm’s goal was not the authentication of narrators, rather he was concerned with mentioning whom among the Shiʿā had authored books.
And we have discussed in another place how not every praise of a narrator necessitates the authentication of a chain, but rather their praise of the narrator must be in terms of his reliability or due to the correctness of his transmission, so if they say: Person so-and-so was proficient in language, it is indeed a praise but it does not necessitate the probative force of what he transmits in terms of ḥadīth, and we have differed from Sayed al-Khoeī in terms of what he has said regarding the probative force of a ḥasan  ḥadīth. And we said, if the praise for the narrator is in terms of his transmission, then a ḥadīth will be reliable and if the praise is other than that, then it will not be reliable. Recently some attendees of the lessons of Shaykh Waḥīd al-Khurāsānī (may Allah preserve him) have transmitted to me that his eminence has also disputed Sayed al-Khoeīs stance on the issue of the probative force of a ḥasan ḥadīth.
And in addition to the issue of Ibn Muʿammar there is also ʿAlī b. Muḥammad b. Masʿada in the chain and he is muhmal , but him being unknown does not harm the reliability of the narration; because the ḥadīth was narrated from him and from Ibn Faḍāl together, and there is also Saʿdān b. Muslim in the chain and he is unknown, but Sayed al-Khoeī has authenticated him based on his name being mentioned in the chains of narration of Kāmil al-Ziyārāt and Tafsīr al-Qummī and it has not been established that their names being mentioned in these chains affirms their reliability, nor is it established that Saʿdān b. Muslim is the same person as ʿAbd al-Raḥmān b. Abī Najrān (and his name is ʿAmru b. Muslim) and we did not find a way to authenticate this, because none of the classical Rijāl scholars objected to them being separate individuals, as we can see by Shaykh al-Ṭūsī and al-Najāshī mentioning separate entries for them so it is far fetched that it is one person. So based on this the narration is weak by its chain.
The third narration: What was transmitted in al-Miṣbāḥ and other books:
On the twentieth of Ṣafar was the return of the camp of al-Ḥusayn (peace be upon him) from Syria to the city of the Messenger (Medina), and it is the day that Jābir b. ʿAbd Allāh al-Ansārī reached the zīyāra of al-Ḥusayn (peace be upon him) and he was the first of the people to visit him
See: Miṣbāḥ al-Mutahajjid (787) and Masār al-Shīʿa (46)
And this narration is mursal, rather it can even be said it has no chain at all in both of the sources.
Regardless of the chain of narrators, the narration speaks of the coincidence of the coming of the camp of Imām al-Ḥusayn from Syria to Medina with the presence of Jābir al-Ansārī with Imām al-Ḥusayn in Karbalā. Now is there in this text a clear and noble Sunnah that must be continued until the Day of Resurrection at this date? Because this is what requires evidence and the narration does not talk about this subject nor even allude to it.
These are the texts I have found regarding this subject, and I have found some contemporary writers state that the act of Imām Zayn al-ʿAbidīn (peace be upon him) and Jābir b. ʿAbd Allāh al-Ansārī is an infallible act, to infer that it is recommended, but arguing for it using this is strange; because the act of an infallible proves the permissibility of something not its recommendation as the scholars of Uṣūl  have established, except if there appears to be an indicator, such as repetition of the act, for example if the infallible was on a journey and prayed, this does not indicate the desirability of prayer at that specific moment, but rather the general desirability that is not specified, and right now the research is regarding the recommendation on the fortieth in specific and not regarding the recommendation of the Zīyāra of Imām al-Ḥusayn (peace be upon him) [in general] even on the fortieth day, because there is no doubt about its general recommendation as we can tell by the many mutawātir  narrations. And the discussion here is based on if the narrations that specify the fortieth are established, but they are not authentic by their chain as we have seen.
As for what you have mentioned in your question on the possibility of relying on them based on their popularity among the later scholars, then this narration – while ignoring the discussion regarding the authoritativeness of this principle – would not be classified as a popular ḥadith, as is well-known among the investigators, as a narration that becomes famous among the later scholars does not reveal the stance of the sharīʿa to us.
Based on this, we conclude that Zīyārat al-Arbaʿīn with its title cannot be established through the narrations, which at most are only three narrations, the first narration has no chain of narrators and there are those who argue for its lack of being an evidence [because of the lack of explicitness of the narration], the second narration in its chain of narrators are three unknown narrators, and the third narration has no indication of the subject in the first place. And the acting of the jurists upon these narrations is not possible other than through the principle of tasāmuḥ  so that their acting on it becomes a remedy for its weakness, based on the principle of al-Jabr al-Sanadi.
Yes, it is possible to rely on the general reports of the zīyāra of Imām al-Ḥusayn (peace be upon him) which are transmitted in multiplicity, so one visits on the twentieth of Ṣafar with the intention of doing a recommended act, without intending to address the zīyāra by a special title, called Zīyārat al-Arbaʿīn, unless it is built on the basis of the principle of leniency, then the second narration is taken because of the requirement of an indication, which is relatively clearer in the second narration, and this principle of leniency is not established according to Sayed al-Khoeī.
As for the saying that Zīyārat al-Arbaʿīn was taken from the Jews, this has not been established with evidence, and even if we were to liken to them by this act, that by itself is not evidence that it has leaked from them to us which leads to a kind of distortion of the image of Zīyārat al-Arbaʿīn, unless there is evidence for this, as the commonalities between Islam, Judaism and Christianity are not few.
In my estimation, the case is dependent on the evidence, and the evidence did not point to the recommendation of it specifically, but it does not prevent zīyāra at this time, taking the reports of general recommendation and with intent of rajāʾ al-matlubiyyah [i.e. in the hope that it is desired by Allah].
My last words here are: There is no need to insist on invalidating some good things in their own right as if one wants to destroy rituals and customs, and I suggest replacing this by clarifying the legitimate reasons to the people, as well as to stop the opposing party from accusing those who want to discuss these matters in a scientific way by questioning their religiosity and beliefs, and instead of all of this it would be better if we all think together about how to develop reviving, awakening and informative programs, to convert the zīyārat of Imām al-Ḥusayn (peace be upon him) – and others – to a large popular Islamic conference for all believers who need it from all over the globe, to decorate the crowded roads with gatherings of literature, poetry, Ḥusayni prose and revolutionary prose, and religious and social programs. And with educative intellectual lectures, gatherings of worship and spirituality, and the meeting of religious references and big personalities with the people, to listen to their concerns and issues and communicate with them and preach to them and guide them, as was the habit of the Imāms of the Ahlulbayt (peace be upon them all) every year during Ḥajj and ʿUmra.
It is of absolute importance today to make more use of these religious occasions, and not to let them pass without making the most out of them.
We need to further rationalise our religious events and ensure the best use of them for our social, political and moral issues today, and to prevent them from turning into mere habits that do not contain meaning or rituals and protocols that we are passing by, because our situation will become – God forbid – like the fasting person described by the ḥadīth of the Holy Prophet ﷺ saying: “The one who is fasting but has no fast except hunger and thirst”.
|↑1||Translators note: There is a slightly older source, Kitāb al-Mazār (53) by Shaykh al-Mufīd (d. 413 AH), he transmitted it in the same way with no chain at all stating “It has been narrated”.|
|↑2||Mursal (disconnected) ḥadīth (Arabic: حدیث مُرسَل) is a terminology in ḥadīth sciences, referring to a ḥadīth with one or more transmitters left out or omitted from the chain.|
|↑3||Authority of Permission or Shaykh al-Ijāza (Arabic: شیخ الاجازة), the plural form Mashāyikh al-Ijāza (مشایخ الاجازة), or Mashīkhat al-Ijāza, (مشیخة الاجازة) refers to a master or a teacher who gave the permission to others to transmit hadiths or books of hadiths.|
|↑4||A ḥadīth that is graded as ḥasan (good) is a ḥadīth with a chain consisting of only trustworthy narrators and 1 or more “praised” narrators, these are narrators for whom we cannot find explicit words from the classical Rijāl authorities regarding their reliability in transmitting, but for whom we can find narrations or statements of them being praised.|
|↑5||A narrator who is mentioned in sources of Rijāl without any comments on his reliability.|
|↑6||Uṣūl al-Fiqh (Arabic: أصول الفقه) is an Islamic discipline that studies the ways of istinbat or deducing the laws of sharīʿa, that is, reliable ways of arriving at such laws by an appeal to the traditional evidence (i.e. Qur’an and ḥadiths) as well as rational evidences.|
|↑7||Generally speaking, a mutawātir ḥadith is a report who’s veracity has been established due to the great amount of chains that point to the ḥadith.|
|↑8||The principle of leniency in evidences for non-obligatory acts (Qā’idah Al-Tasāmuḥ Fī Adilat Al-Sunan)|
Principle of Leniency in Deducing Proofs for Recommended Acts (al-Tasamuh fi Addilat al-Sunan) | Thaqalayn Blog
The Principle of Leniency in Evidences for Non-Obligatory Acts and its Jurisdiction – The View of Shi’a Jurists from the Occultation to the Fourteenth Century After Hijra | Syed Mohammad Hadi Rizvi