He cannot control his urine and he is very old; should he fast and pray?
Question

                My father has become old, 105 years of age, and he has lost his memory, sometimes he recognizes us and sometimes he does not. In the last few years he has become unable to control his urine. We change his clothes more than once each day. Does he have to pray even though he cannot remain pure? Should we make him fast?.
Praise be to Allah.
    The ruling concerning your father differs depending on his 
    state of mind. If he loses his reason and his memory then he should not be 
    told to purify himself or to pray or fast, but when his mind is present and 
    focused and his memory is with him, then he should be told to do the duties 
    enjoined by sharee’ah as best as he can, without causing himself undue 
    hardship. 

    Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have 
    mercy on him) was asked: 

    Do those who have lost their memory, the feeble-minded, young 
    children and the insane have to fast? 

    He replied: 

    Allaah has enjoined acts of worship on man if he is able to 
    bear that obligation, by being of sound mind and able to understand things. 
    But if he is not of sound mind then he does not have to do those acts of 
    worship. So the insane and young children who have no powers of discernment 
    do not have to do these acts of worship. This is by the mercy of Allaah, may 
    He be glorified and exalted. The same applies to the feeble-minded person 
    whose mind is affected in some way but not to the degree of insanity and the 
    elderly person who has lost his memory, as this questioner says, do not have 
    to fast, pray or purify themselves, because the one who has lost his memory 
    is like a small child who has no power of discernment, so the duties of 
    Islam are waived for him and he does not have to purify himself or pray, nor 
    does he have to fast. With regard to the financial obligations, they are 
    required of his wealth even in this case, so zakaah – for example – must be 
    paid by his guardian on his wealth if it reaches the amount at which zakaah 
    becomes due, because the obligation of zakaah is connected to wealth, as 
    Allaah says (interpretation of the meaning): 

    “Take Sadaqah (alms) from their wealth in order to purify 
    them and sanctify them with it, and invoke Allaah for them. Verily, your 
    invocations are a source of security for them; and Allaah is All-Hearer, 
    All-Knower”

    [al-Tawbah 9:103]

    He did not say “take it from them.” 

    And the Prophet  (peace and blessings of Allaah be upon 
    him) said to Mu’aadh (may Allaah be pleased with him) when he sent him to 
    Yemen: “Teach them that Allaah has enjoined on them sadaqah (charity) from 
    their wealth, to be taken from their rich and given to their poor.” He said, 
    “Charity from their wealth” and explained that it is to be taken from their 
    wealth, even though it is to be taken from the owner of the wealth.  
Whatever the case, the 
    financial obligations are not waived for a person in this case, but the 
    religious obligations such as prayer, purification and fasting, are waived 
    in the case of people like this man, because he does not have any powers of 
    understanding. 

    Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen, 
    10, question no. 40. 

    The Shaykh (may Allaah have mercy on him) was also asked: 

    What is the ruling on fasting for one who is sane sometimes 
    and insane at other times, or who is incoherent one day and focused another 
    day? 

    He replied: 

    The ruling changes according to the reason. At times when he 
    is conscious and aware, he has to fast, and at times when he is insane and 
    incoherent, he does not have to fast. If we assume that he is insane one day 
    and sane another, or incoherent one day and focused another, then on the 
    days when he is focused he has to fast, and on the days when he is 
    incoherent he does not have to fast. 

    Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen, 
    10, question no. 43. 

    And Allaah knows best.