Is worship obligatory for one who does not retain awareness of the acts of worship?

Question:
May Allah reward you with good, O Shaykh. The questioner, Hasan from Eastern Qaisumah, says: I have an elderly uncle who has suffered several strokes in his head and other illnesses. Now, for about a year, he does not know the prayer. We teach him him, but to no avail. Now he says that in the last Ramadan, we would tell him, "This is Ramadan, you must fast," and he would fast and break his fast on some days. What is the ruling for one in this condition?

Answer:
If his mind is affected and he does not know, he does not know the time and does not retain awareness of the act of worship, then he owes nothing, because he is not accountable. But if his mind is with him, and he knows the act of worship and knows the time, but is only affected at times, then it is obligatory for him to fast and it is obligatory for him to pray. If he leaves off some of the fasting or the prayer during the time he is affected, he must make it up when he recovers and his mind returns to him. But if his condition and the loss of his mind are permanent, then he owes nothing. Yes.