Ruling on a person who loses reason at times

Q 1: My grandfather is about one hundred and fifty years old. One year ago he started to lose his mental capacity at times. Moreover, he is now unable to move and consequently unable to perform the obligatory Salah (Prayer). It may be worth mentioning that my grandfather has a continuous and uncontrollable discharge of excrement and urine. My question here is whether it is Wajib (obligatory) on him to perform Salah? It is worth mentioning that my grandfather becomes mentally disordered only sometimes, not all the time. Provide us with your beneficial answer please. May Allah reward you with the best.

A: At times when your grandfather has his full mental capacity, it is Wajib on him to perform Salah as much as he can. This is because Allah (Exalted be He) says: So keep your duty to Allâh and fear Him as much as you can Moreover, the Prophet (peace be upon him) said: When I command you to do anything, do of it as much as you possibly can. Your grandfather has to clean himself and make Wudu' (ablution), or make Tayammum (dry ablution) in case of his inability to use water, or (Part No. 5; Page No. 14) just to perform Salah without making any Wudu' or Tayammum in case of his inability to make Tayammum. Besides, your grandfather has to perform Salah standing, sitting in case of his inability to stand up, lying down on his sides in case of his inability to sit, or lying down on his back in case of his inability to lie down on his side. This is also supported by Allah's saying: So keep your duty to Allâh and fear Him as much as you can In addition, the Prophet (peace be upon him) said: Pray while standing and if you can't, pray while sitting and if you can't do even that, then pray lying on your side. (Related by Al-Bukhari in his Sahih 'authentic' Book of Hadith) Al-Nasa'y related the same with the addition of: "and if you can't, pray lying on your back."On the other hand, your grandfather does not have to perform Salah at times when he is mentally disordered. He does not even have to make up for it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.