2 Samuel 13:4 (KJV)

And Amnon was so vexed, that he fell sick for his sister Tamar; for she was a virgin; and Amnon thought it hard for him to do any thing to her.

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

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

And Jonadab said unto him, Lay thee down on thy bed, and make thyself sick: and when thy father cometh to see thee, say unto him, I pray thee, let my sister Tamar come, and give me meat, and dress the meat in my sight, that I may see it, and eat it at her hand.

So Amnon lay down, and made himself sick: and when the king was come to see him, Amnon said unto the king, I pray thee, let Tamar my sister come, and make me a couple of cakes in my sight, that I may eat at her hand.