Can a hadeeth be accepted from a narrator who suffered from mental problems?
Question

                In mutatawir (multiple narrators) hadith is it a condition that all the narrators to memorise the hadith or could they read it from paper to the next level. What happens if a narrator of mutatawir has some form of mental deficiency?.
Praise be to Allah.
    The mutawaatir hadeeth is that which was narrated by a large 
    number in such a way that they could not have agreed on a lie, from a 
    similarly large number, and so on until the end of the isnaad (chain of 
    narrators), and their report is based on one of the five senses. Hence there 
    is no room for confusion or error on the part of the narrator, because if we 
    assume that a narrator had a poor or weak memory, the large number of 
    narrators and the fact that they all narrated the same report strengthens 
    the hadeeth.. 

    As for the narrator of the hadeeth himself, if he suffered 
    from mental problems, the scholars of hadeeth stipulated stringent 
    conditions for accepting the report of a narrator so as to confirm that he 
    was free of any flaws or mistakes. They stipulated that he should be a 
    Muslim of sound mind with a precise memory if he narrated from memory, or 
    that he should be known to be careful and precise in his writing if he 
    narrated from his writing, and that he should be a man of piety who kept 
    away from sin and was not known for evildoing or openly committing sin. 

    They also stipulated that he should be free of anything that 
    would undermine dignity; his conduct and attitude should be proper and he 
    should not behave in an odd or suspicious manner, such as wearing improper 
    clothing in a public gathering, and the like. 

    Once they established that the narrator was free of these 
    faults, they would compare his reports to the reports of other scholars who 
    were known for precision in narration, so as to make sure that his hadeeth 
    was free from any oddities or flaws, i.e., errors or anything that 
    contradicted the reports of anyone who was more credible than him, either in 
    the number of reports that he narrated or in his memory or precision. This 
    matter could be so subtle that it is very difficult for many seekers of 
    knowledge to understand, but they should try their utmost to research and 
    examine the matter until they become certain as to the soundness of the 
    narrator or the soundness of his reports. Hence we find that the scholars 
    stated that the conditions of a hadeeth being saheeh (sound) are five: 

    1.Good character of all the 
    narrators, which means that all of them should be free of anything that may 
    be regarded as evildoing and anything that may undermine their dignity.

    2.Precise memory of the narrators 
    who narrated the hadeeth.

    3.No interruptions in the chain 
    of narrators (isnaad) from beginning to end, in the sense that each narrator 
    heard it from the narrator above him in the chain.

    4.The hadeeth should be free of 
    anything odd in its isnaad or text. What is meant by “odd” is anything in 
    which the narrator contradicts a narrator who is more credible than him.

    5.The hadeeth should be free of 
    flaws in its isnaad or text. The “flaw” is a subtle reason that could 
    undermine the soundness of the hadeeth. This is only known to well-versed 
    scholars.

    Thus it becomes clear that there is no room for accepting the 
    hadeeth of the narrator who suffered from any mental disorder that could 
    affect his memory and narration. The same applies if he has any 
    psychological problems that means that he is not qualified to narrate a 
    hadeeth or teach it; in that case he is not to be relied upon when he 
    narrates from the Messenger of Allah (blessings and peace of Allah be upon 
    him). Rather the reports of any narrator cannot be accepted unless the 
    scholars of this field testify that he was well versed and qualified, and 
    that his hadeeth is acceptable. And Allah knows best. 

    See: Tadreeb al-Raawi by al-Suyooti, 1/68-75, 155; 
    al-Nukat ‘ala Ibn al-Salaah by Ibn Hajar, 1/480.