1 Samuel 18:17-21

17Then Saul said to David, "Here is my elder daughter Merab. I will give her to you for a wife. Only be valiant for me and fight the Lord's battles." For Saul thought, "Let not my hand be against him, but let the hand of the Philistines be against him."

18And David said to Saul, "Who am I, and who are my relatives, my father's clan in Israel, that I should be son-in-law to the king?"

19But at the time when Merab, Saul's daughter, should have been given to David, she was given to Adriel the Meholathite for a wife.

20Now Saul's daughter Michal loved David. And they told Saul, and the thing pleased him.

21Saul 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."