1 Samuel 18:17-20 New King James Version (NKJV)
David Marries Michal
17 Then Saul said to David, “Here is my older daughter Merab; I will give her to you as a wife. Only be valiant for me, and fight the Lord’s battles.” For Saul thought, “Let my hand not be against him, but let the hand of the Philistines be against him.”
18 So David said to Saul, “Who am I, and what is my life or my father’s family in Israel, that I should be son-in-law to the king?” 19 But it happened at the time when Merab, Saul’s daughter, should have been given to David, that she was given to Adriel the Meholathite as a wife.
20 Now Michal, Saul’s daughter, loved David. And they told Saul, and the thing pleased him.
1 Samuel 18:27 New King James Version (NKJV)
27 therefore David arose and went, he and his men, and killed two hundred men of the Philistines. And David brought their foreskins, and they gave them in full count to the king, that he might become the king’s son-in-law. Then Saul gave him Michal his daughter as a wife.