What is the ruling regarding the prayer of an elderly father who cannot prostrate except once due to his weak memory, and does not believe anyone who reminds him?

If a person reaches old age and his perception and intellect remain intact, then prayer is obligatory upon him, and he prays in the manner he is able to, according to the Prophet's saying: "Pray standing; if you are unable, then sitting; if you are unable, then on your side." For intellect is the basis of religious obligation. If he prays alone, then what matters is his conviction, and Allah will overlook [shortcomings] due to his effort. It is preferable to help him perform congregational prayers in the mosque if possible. However, if he becomes unable to perceive due to old age, then prayer is not obligatory upon him, and he prays in his condition. If he perceives at times and not at other times, then he is required to pray when he perceives.