1 Samuel 18:26

18:26 So his servants told David these things and David agreed to become the king’s son-in-law. Now the specified time had not yet expired

1 Samuel 16:1

Samuel Anoints David as King

16:1 The Lord said to Samuel, “How long do you intend to mourn for Saul? I have rejected him as king over Israel. Fill your horn with olive oil and go! I am sending you to Jesse in Bethlehem, for I have selected a king for myself from among his sons.”

1 Samuel 18:27

18:27 when David, along with his men, went out and struck down two hundred Philistine men. David brought their foreskins and presented all of them to the king so he could become the king’s son-in-law. Saul then gave him his daughter Michal in marriage.