The third condition: that he be of sound mind.

The Shaykh : The third condition is that he be of sound mind. The opposite of the sane person is the insane, or, in a broader term, the opposite of the sane person is one who has no intellect, whether the loss of intellect is due to insanity, an accident, old age, or an illness that has befallen him. If a person’s intellect is lost for any reason, then fasting is not obligatory upon him, based on the saying of the Prophet (peace and blessings be upon him): Based on this, if a man grows old until he becomes incoherent, not knowing what he says or recognizing anything, and his intellect descends to that of a child, then in this state, fasting is not obligatory upon him, nor is feeding [the poor] obligatory upon him, just as prayer and ritual purity are not obligatory upon him. As for zakah, it is obligatory in his wealth, because the place of zakah is the wealth, not the person’s liability.