Al-Hafiz Ibn Hajar holds that a narration from a person unknown by identity cannot be strengthened, whereas a mursal hadith can be strengthened; what is the difference between the two?

The questioner : Our esteemed Shaykh, Al-Hafiz Ibn Hajar holds that a narration from a person unknown by identity cannot be strengthened, whereas a mursal hadith can be strengthened; what is the difference between the two? Since a narrator is missing from the mursal, and he is not known by identity or condition?

The Shaykh : Yes, the mursal hadith shares a commonality with the hadith containing a narrator unknown by identity, and it differs from it in one aspect. It shares one aspect and differs in another. It shares the aspect he pointed toThe questioner : ; that when the one who sends the hadith (al-mursil) says: The Messenger of Allah (peace and blessings be upon him) said, and he certainly did not meet the Messenger of Allah (peace and blessings be upon him), then without a doubt, in this situation, there must be an intermediary or more than one intermediary between him and the Messenger of Allah (peace and blessings be upon him). As for the unknown person, he is a specific individual whose identity is not known and whose integrity is not established; therefore, the use of his hadith as evidence, or even as a citation, is dropped. As for the mursal, although it contains, as we mentioned, an unknown man or more, it differs from the unknown in another aspect; which is that many scholars of hadith and jurisprudence used the mursal hadith as evidence; because some of them held in their minds that this Tabi'i who sent the hadith is, by preponderant probability, one who received it from a Companion of the Prophet (peace and blessings be upon him), and all the Companions are trustworthy according to the people of the Sunnah; so it does not harm that they are not named. Therefore, all these scholars agreed, whether they used the mursal as evidence or not; they all agreed that the Tabi'i who sends the hadith, usually when he says: A man from the Companions of the Messenger of Allah (peace and blessings be upon him) narrated to me, his hadith is valid; because this Companion, even if not named, the Companions are trustworthy.
And since the probability wavers that the Tabi'i who sent the hadith from the Prophet (peace and blessings be upon him) may have taken it from a Companion, and it is possible that he took it from a Tabi'i, and this Tabi'i is not like that Companion. The Companions, as we mentioned, are all trustworthy, whereas the Tabi'un are not described as all being trustworthy. Because of this possibility, some scholars of hadith said that the mursal is not used as evidence; due to the possibility that he took it from a Tabi'i and not from a Companion. As for the unknown, it is known that he did not take it except from the one who will establish... his hadith; he may be a Tabi'i or below that; meaning: if the unknown is a Tabi'i, now we picture another scenario; if Sa'id ibn al-Musayyib or al-Musayyib (and the first is more correct linguistically) said: A man narrated to me from Abu Hurayrah; this is an unknown person who is not used as evidence if we include him in the rule of not using, or even not citing, the hadith of the unknown. Here, it may take another ruling; why?
Because this unknown is a Tabi'i, so every unknown has the ruling mentioned previously. But if this unknown is from the Tabi'un, lying was not famous among them, nor had poor memory spread to them. Therefore, we rarely find one of the Tabi'un mentioned for poor memory. This exists, but it is rare compared to those who came after them. If we observe the level of the unknown and the difference between the unknown Tabi'i and the Tabi'i below him, then the point of those who said using the mursal hadith as evidence becomes clear to us; because, as we mentioned, it is either from an unnamed Companion, in which case it is a valid hadith, or it is from a Tabi'i; the unknown Tabi'un are not subject to the dropping of citation like those who came after them. This is the difference that can be observed in the scholars' distinction between the unknown by knowledge and the unknown by identity if he is a Tabi'i, and their use of the mursal as evidence by some scholars, among them, for example, Imam Malik, the Imam of the City of Migration, who used the mursal hadith as evidence despite the possibility that he took it from a Tabi'i. The reason for this is nothing but what we mentioned earlier regarding the preponderance of good opinion of the Tabi'i; in terms of his integrity and his memory.
This is what can be mentioned as an answer to this question.