1 Samuel 18:20-21

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

And Saul said, I will give him her, that she may be a snare to him, and that the hand of the Philistines may be against him. Wherefore Saul said to David, Thou shalt this day be my son in law in the one of the twain.