What should I do about my father, who is over sixty and unable to pray due to his illness, even though he has memorized the entire Qur’an?

The obligation of prayer does not cease for a Muslim as long as they are of sound mind. A Muslim prays according to their ability: standing, if unable, then sitting, if unable, then on their side. A sick person gestures for bowing and prostration, making their prostration lower than their bowing. It is obligatory to advise and guide those who abandon prayer with gentleness and wisdom, clarifying the Shariah texts regarding the importance of prayer, and to frequently supplicate for their guidance.