1 Samuel 18:23

21And 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.

22And Saul commanded his servants, saying, Commune with David secretly, and say, Behold, the king hath delight in thee, and all his servants love thee: now therefore be the king’s son in law.

23And Saul’s servants spake those words in the ears of David. And David said, Seemeth it to you a light thing to be a king’s son in law, seeing that I am a poor man, and lightly esteemed?

24And the servants of Saul told him, saying, On this manner spake David.

25And 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.