2 Samuel 13:3-5

3But Amnon had a friend, whose name was Jonadab, the son of Shimeah David’s brother: and Jonadab was a very subtil man.

4And he said to him, Why art thou, being the king’s son, pining from day to day? wilt thou not tell me? And Amnon said to him, I love Tamar, my brother Absalom’s sister.12

5And Jonadab said to him, Lay thee down on thy bed, and pretend that thou art sick: and when thy father cometh to see thee, say to him, I pray thee, let my sister Tamar come, and give me food, and prepare the food in my sight, that I may see it, and eat it at her hand.