Rulings pertaining to the person suffering from amnesia
29-1-2016 | IslamWeb
Question:
Assalaamu alaykum. What is the ruling in Islam about amnesia? Is it possible for a person to forget everything about himself (as seen in movies)? What if a practicing Muslim forgets all about his past and then becomes a non-Muslim? Would he be considered like the insane person?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad 
is His slave and Messenger.
A person who suffers from amnesia, a total loss of memory, as you have mentioned in the question, forgetting all about his name and family and unable to recall any of that and the like, is declared mentally incompetent for religious assignments. If he commits an act of disbelief that would take the sane doer out of the fold of Islam, then he is not declared a disbeliever. This is because the Prophet said, "The pen is lifted from (writing the deeds of) three people (i.e. they are excused by Allaah): a sleeping person till he wakes up, a child till he reaches puberty, and an insane person till he can reason." [Ahmad, Abu Daawood, An-Nasaa'i, and Ibn Maajah - Al-Haakim grades it saheeh (sound)]
The Kuwaiti Encyclopedia of Fiqh reads:
"Muslim jurists reached a consensus about the fact that insanity is like unconsciousness and sleep; rather, it is more severe in the loss of free will. For the one who is unconscious or sleeping, all his verbal statements, such as divorce, embracing Islam, renouncing Islam, selling, buying, etc., are invalid. So it is more appropriate that such statements be invalid in the case of insanity because the insane person has no power of reasoning or discernment or competence. They quoted the following words of the Prophet as evidence for this: 'The pen is lifted from (writing the deeds of) three people (i.e. they are excused by Allaah): a sleeping person till he wakes up, a child till he reaches puberty, and an insane person till he can reason...' The same applies to all verbal statements because of the potential harm."
Scholars highlighted that a person suffering from amnesia is held at the same status of the minor below the age of distinction in terms of the relevant sharee'ah rulings. Shaykh Ibn ʻUthaymeen 
wrote, "The elderly person who has lost his memory, as this questioner says, does not have to fast, pray or purify himself, because the one who has lost his memory is like a small child who has no power of discernment, so the religious assignments are waived for him and he does not have to purify himself or pray, nor does he have to fast..."
If the mentally challenged person has not reached the level of complete insanity, yet he is labeled as 'maʻtooh' (imbecile person) as per the sharee'ah, then he is also declared incompetent for religious assignments. The Kuwaiti Encyclopedia of Fiqh reads, "Linguistically, the term 'ʻatah' (imbecility) denotes loss of the power of discernment or reason but not to the extent of insanity. In Islamic terminology, ʻatah refers to the condition entailing the impairment of the mind; the actions of such a 'maʻtooh' sometimes demonstrate sanity and sometimes insanity."
The maʻtooh person is incompetent for religious duties according to the jurists who treat him like the discerning minor. In his book At-Tashreeʻ Al-Jinaa’i (Criminal Law in Islam), Abdul-Qaadir ʻOudah, may Allaah have mercy upon him, said, "Muslim jurists define the maʻtooh, or imbecile, as a person with a low level of comprehension, confounded speech, and impaired judgment, whether the condition was inborn or following an illness. It is deduced from this definition that ʻatah (imbecility) is the least degree of insanity. It can be said that insanity leads to total loss of mind or mental disturbance whereas ʻatah leads to mental weakness of varying degrees but remains within the limits of the discerning minor..." [At-Tashreeʻ Al-Jinaa’i]
The maʻtooh is incompetent for religious assignments; the Prophet said, "The pen is lifted from writing the deeds of three: a sleeping person till he wakes up, a child till he reaches puberty and a maʻtooh till he can reason." [At-Tirmithi and others - Al-Albaani graded it saheeh (sound)]
Shaykh Ibn ʻUthaymeen wrote, "Those mentally impaired are declared incompetent for religious assignments; therefore, the insane and young person below the age of distinction, and even the child who has not reached puberty, are all incompetent for religious assignments. This is a manifestation of the mercy of Allaah. The same ruling applies to the maʻtooh, or imbecile, who is mentally challenged or retarded yet has not reached insanity..."
Allaah knows best.