1 Samuel 18:25
And Saul said, Thus shall ye say to David, The king desireth not any dowry, but an hundred foreskins of the Philistines, to be avenged of the king’s enemies. But Saul thought to make David fall by the hand of the Philistines. And Saul said, Thus shall ye say to David, The king desireth not any dowry, but an hundred foreskins of the Philistines, to be avenged of the king’s enemies. But Saul thought to make David fall by the hand of the Philistines.
Saul offered his daughter Michal in marriage to David as a snare rather than as an honor, making the union conditional on a bloody service instead of a customary bride price. He demanded evidence that David had slain a set number of Philistines, presenting the requirement as vengeance against the king's enemies. His secret purpose was that David would be cut down by Philistine hands in attempting the feat. David instead survived the encounter and came back triumphant, so the plot intended for his ruin elevated him to the standing of the king's son-in-law.