1 Samuel 18:18-22

But David said to Saul, “Who am I, and who is my family, or my father’s family in Israel, that I should be the king’s son-in-law?”

So it came about at the time that Merab, Saul’s daughter, was to be given to David, that she was given instead to Adriel the Meholathite as a wife. David Marries Saul’s Daughter

Now Michal, Saul’s daughter, loved David. When they informed Saul, the thing was pleasing to him.

For Saul thought, “I will give her to him so that she may become a trap for him, and that the hand of the Philistines may be against him.” Therefore Saul said to David, “For a second time you may become my son-in-law, today.”

Then Saul commanded his servants, “Speak to David in secret, saying, ‘Behold, the king delights in you, and all his servants love you; now then, become the king’s son-in-law.’ ”