1 Samuel 18:21-22, 29

Saul thought, “Let me give her to him, that she may be a snare for him and that the hand of the Philistines may be against him.” Therefore Saul said to David a second time, “You shall now be my son-in-law.” And Saul commanded his servants, “Speak to David in private and say, ‘Behold, the king has delight in you, and all his servants love you. Now then become the king’s son-in-law.’”

Saul was even more afraid of David. So Saul was David’s enemy continually.