2 Samuel 13:3-5

3And Amnon had a friend whose name was Jonadab, the son of Shimeah David's brother; and Jonadab was a very shrewd man.

4And he said to him, Why dost thou, the king's son, get thinner from morning to morning? Wilt thou not tell me? And Amnon said to him, I love Tamar, my brother Absalom's sister.

5And Jonadab said to him, Lay thee down on thy bed and feign thyself sick; and when thy father comes to see thee, say to him, I pray thee, let my sister Tamar come, and give me food, and dress the food in my sight, that I may see it, and eat it from her hand.