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 shrewd (cunning) man.

4He said to Amnon, “Why are you, the king’s son, so depressed morning after morning? Will you not tell me?” And Amnon said to him, “I am in love with Tamar, my [half-] brother Absalom’s sister.”

5Jonadab said to him, “Go to bed and pretend you are sick; and when your father [David] comes to see you, say to him, ‘Just let my sister Tamar come and serve me food, and let her prepare it in my sight, so that I may see it and eat it from her hand.’ ”