Leviticus 18:7

The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she [is] thy mother; thou shalt not uncover her nakedness.

Ver. 7. She is thy mother.] And so it is against nature to lie carnally with her. Aristotle a tells of a camel that killed his keeper for causing him to cover his dam, and of a horse that cast himself down headlong after he had done the like.

a Hist. Animal., lib. ix. cap. 47.