Prayer of an elderly person who has reached the stage of senility
Question

                My mother is 61 years old and she is looking after my grandfather who has reached the age of 90-odd. A long time ago he began to lose his mind and he started imagining things that are not real. He has no sense of time, and when he gets up to pray and we tell him that it is time for Zuhr, for example, we find him praying Maghrib or Fajr. He calls out to my mother in the middle of the night, telling her to get up and make him breakfast or help him get up to pray ‘Asr, for example. My question is: Does my grandfather have to pray or is it waived in his case? 

My grandfather sometimes calls my mother repeatedly for no reason, and sometimes he asks her what time it is and sometimes he tells her some historical story. My mother is also getting on in years and she cannot keep getting up and going to his room. If she is certain that he does not need anything and that she has met all his needs of food, wudoo’, prayer etc, can she refrain from answering him without incurring sin? Especially since he calls her a lot in the middle of the night.
Praise be to Allah.
    Firstly: 

    If the matter is as you describe, then your grandfather is 
    not obliged to pray, because of his losing his mind, The Prophet  (peace 
    and blessings of Allaah be upon him) said: “The Pen has been lifted from 
    three: from the sleeping person until he wakes up, from the minor until he 
    grows up, and from the insane person until he comes to his senses.” Narrated 
    by Abu Dawood (4403), al-Tirmidhi (1423), al-Nasaa’i (3432) and Ibn Maajah 
    (2041). Abu Dawood said: It was narrated by Ibn Jurayj from al-Qaasim ibn 
    Yazeed from ‘Ali (may Allaah be pleased with him) from the Prophet  
    (peace and blessings of Allaah be upon him), and he added: “And the one who 
    is senile.” This hadeeth was classed as saheeh by al-Albaani in Saheeh 
    Abi Dawood. 

    Senility refers to when a person loses his mind as the result 
    of reaching a great age. It is stated in ‘Awn al-Ma’bood that the 
    report which mentions senility is da’eef (weak) because of the isnaad, but 
    something which suggests that the meaning is valid was narrated from 
    al-Subki. Al-Subki said: Senility may be added to these three, and it is 
    valid. What is meant thereby is an elderly man who has lost his mind due to 
    his great age. An old man may become confused and unable to distinguish 
    things, which may mean that he is no longer accountable, but he is not 
    described as insane, because an insane person may be treated whereas a 
    senile person cannot be treated. Hence it does not say in the hadeeth “until 
    he recovers”, because in most cases he cannot recover from it, until he 
    dies. If he does recover from it sometimes and comes back to his senses, 
    then he is accountable again. End quote. 

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) 
    explained that senility means that one is no longer accountable: Fasting is 
    not obligatory unless certain conditions are met: one, being of sound mind; 
    two, being an adult; three, being Muslim; four, being able to do it; five, 
    not being a traveller; six, being free of menses and postpartum bleeding 
    (nifaas) in the case of women. 

    1 – Being of sound mind, the opposite of which is having lost 
    one’s mind, whether that is due to insanity or senility, i.e., old age, or 
    because of an accident which has caused one to lose one’s mind and sense of 
    awareness. Such a person is not obliged to do anything because he has lost 
    his mind. Based on this, the old man who has reached the stage of senility 
    is not obliged to fast or feed poor persons instead, because he lost all 
    sense of reason. Similarly the one who loses consciousness due to an 
    accident etc is not obliged to fast or feed poor persons instead, because he 
    is not of sound mind. End quote from Liqa’ al-Baab il-Maftooh. 

    To conclude, the person who has reached the stage of senility 
    and has no sense of time and cannot distinguish between the prayers is not 
    obliged to pray. 

    Secondly: 

    If your mother has taken care of what your grandfather needs, 
    such as food and drink, etc, and she thinks it most likely that his calling 
    for her is not due to some need, and it is just because of his senility, 
    then there is no sin on her if she does not answer him, especially since 
    that is causing her hardship. 

    And Allaah knows best.