1 Samuel 16:1-13 (NASB):

Now the Lord said to Samuel, “How long will you grieve over Saul, since I have rejected him from being king over Israel? Fill your horn with oil and go; I will send you to Jesse the Bethlehemite, for I have selected a king for Myself among his sons.” But Samuel said, “How can I go? When Saul hears of it, he will kill me.” And the Lord said, “Take a heifer with you and say, ‘I have come to sacrifice to the Lord.’ You shall invite Jesse to the sacrifice, and I will show you what you shall do; and you shall anoint for Me the one whom I designate to you.” So Samuel did what the Lord said, and came to Bethlehem. And the elders of the city came trembling to meet him and said, “Do you come in peace?” He said, “In peace; I have come to sacrifice to the Lord. Consecrate yourselves and come with me to the sacrifice.” He also consecrated Jesse and his sons and invited them to the sacrifice.

When they entered, he looked at Eliab and thought, “Surely the Lord’s anointed is before Him.” But the Lord said to Samuel, “Do not look at his appearance or at the height of his stature, because I have rejected him; for God sees not as man sees, for man looks at the outward appearance,but the Lord looks at the heart.” Then Jesse called Abinadab and made him pass before Samuel. And he said, “The Lord has not chosen this one either.” Next Jesse made Shammah pass by. And he said, “The Lord has not chosen this one either.” Thus Jesse made seven of his sons pass before Samuel. But Samuel said to Jesse, “The Lord has not chosen these.” And Samuel said to Jesse, “Are these all the children?” And he said, “There remains yet the youngest, and behold, he is tending the sheep.” Then Samuel said to Jesse, “Send and bring him; for we will not sit down until he comes here.”

So he sent and brought him in. Now he was ruddy, with beautiful eyes and a handsome appearance. And the Lord said, “Arise, anoint him; for this is he.” Then Samuel took the horn of oil and anointed him in the midst of his brothers; and the Spirit of the Lord came mightily upon David from that day forward. And Samuel arose and went to Ramah.