Is it permissible for a mother to look at her son or for a son to look at his mother with lust, and is it permissible for a son to fondle his mother as if he were fondling his wife?

Jurists and sound minds have agreed on the prohibition of incest and its preliminaries. A man is permitted to look at what is commonly uncovered of his unmarriageable kin (mahārim), such as the neck, head, hands, and feet, but it is forbidden to look with lust, and it is forbidden to look at what is usually covered, such as the chest and back.