1 Samuel 15:10-18

Then the word of the LORD came to Samuel, saying, “I regret that I made Saul king, for he has turned away from following Me and has not carried out My commands.” Samuel was angry [over Saul’s failure] and he cried out to the LORD all night. When Samuel got up early in the morning to meet Saul, he was told, “Saul came to Carmel, and behold, he set up for himself a monument [commemorating his victory], then he turned and went on and went down to Gilgal.” So Samuel came to Saul, and Saul said to him, “Blessed are you of the LORD. I have carried out the command of the LORD.” But Samuel said, “What then is this bleating of the sheep in my ears, and the lowing of the oxen which I hear?” Saul said, “They have brought them from the Amalekites, for the people spared the best of the sheep and oxen to sacrifice to the LORD your God; but the rest we have destroyed completely.” Then Samuel said to Saul, “Stop, and let me tell you what the LORD said to me last night.” Saul said to him, “Speak.” Samuel said, “Is it not true that even though you were small (insignificant) in your own eyes, you were made the head of the tribes of Israel? And the LORD anointed you king over Israel, and the LORD sent you on a mission, and said, ‘Go, totally destroy the sinners, the Amalekites, and fight against them until they are eliminated.’