TSK · Deuteronomy 27:22

“‘If a man has marital relations with his sister, whether the daughter of his father or his mother, so that he sees her nakedness and she sees his nakedness, it is a disgrace. They must be cut off in the sight of the children of their people. He has exposed his sister’s nakedness; he will bear his punishment for iniquity.

So Tamar went to the house of Amnon her brother, who was lying down. She took the dough, kneaded it, made some cakes while he watched, and baked them.