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

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.