He is mentally ill and does not pray or fast; what is the ruling?
Question

                What is the ruling on a person who is psychotic bipolar and does not offer prayers, or fast? Whenever he is advised to do so he says that he is ill and Allah will forgive him but actually the person is not physically disable to offer prayer. Also, what about his sense of judgement? He thinks he is always right even though when sometimes he is not, and he thinks others are always wrong and he backbites them.
Praise be to Allah.
      Firstly: 

    We ask Allah to heal this sick person from this sickness that 
    he is suffering, and we ask Him, may He be glorified, to guide us and him to 
    the truth and the right path, for He is able to do that. 

    Secondly: 

    The conditions of accountability with regard to commands and 
    prohibitions are being an adult and being of sound mind. When a person 
    becomes an adult of sound mind, it becomes obligatory for him to do what is 
    enjoined of praying, fasting, giving zakaah, performing Hajj and other 
    obligatory duties, and he is also obliged to avoid things that are 
    prohibited. 

    It says in Fataawa al-Lajnah ad-Daa’imah (vol. 2, 
    6/370): Prayer is obligatory upon the individual and is not waived under any 
    circumstances so long as he is of sound mind, because the conditions of 
    accountability are being an adult and being of sound mind. The command to 
    pray is not waived because of loss of a limb or physical faculty, or because 
    of sickness, or similar problems, because of the general meaning of the 
    Qur’an and Sunnah, and scholarly consensus to that effect. But if a person 
    suffers some physical harm and is not able to do all the obligatory actions 
    and essential parts of the prayer, then he may pray according to what he is 
    able to do. End quote. 

    Based on that, if this mental illness does not affect the 
    person’s reasoning or consciousness, as appears to be the case in the 
    situation mentioned, then it is obligatory for him to pray and fast, because 
    he is still accountable. 

    But if he loses his mind sometimes, and is of sound mind 
    sometimes, then he is excused at the times when he loses his mind, but when 
    he comes back to his senses the excuse is no longer applicable, and he has 
    to offer the prayer that is currently due and make up the prayers that he 
    missed during the time when he lost his mind. 

    What you must do is advise this man and remind him of the 
    great importance of prayer and fasting, and tell him that the one who does 
    not do these duties without any excuse is in grave danger; in fact keeping 
    away from remembrance of Allah is one of the greatest causes of mental 
    illness, as Allah, may He be exalted, says (interpretation of the meaning):

    “But whosoever turns away from My Reminder (i.e. neither 
    believes in this Quran nor acts on its orders, etc.) verily, for him is a 
    life of hardship”

    [Ta-Ha 20:124].

    Allah, may He be glorified, also tells us of the means of 
    attaining peace of mind, as He says (interpretation of the meaning):

    “Verily, in the remembrance of Allah do hearts find rest”

    [ar-Ra ‘d 13:28]. 

    It should be noted that the individual is responsible for all 
    of his deeds before his Lord, may He be glorified and exalted, so long as he 
    is aware of what he is saying or doing. His illness is not an excuse for him 
    to commit whatever sins he wants, such as neglecting the prayer, backbiting 
    and spreading malicious gossip. … The individual has no argument against his 
    Lord, may He be glorified and exalted; rather Allah has the perfect proof 
    and argument against all His creation. 

    We ask Allah to set the affairs of the Muslims straight and 
    to bring them back to Him. 

    And Allah knows best.