2 Samuel 13:2, 4

And Amnon was so tormented that he made himself ill because of his sister Tamar, for she was a virgin, and it seemed impossible to Amnon to do anything to her.

And he said to him, “O son of the king, why are you so haggard morning after morning? Will you not tell me?” Amnon said to him, “I love Tamar, my brother Absalom’s sister.”