1 Samuel 15:17-19
17-19And Samuel told him. "When you started out in this, you were nothing— and you knew it. Then God put you at the head of Israel—made you king over Israel. Then God sent you off to do a job for him, ordering you, 'Go and put those sinners, the Amalekites, under a holy ban. Go to war against them until you have totally wiped them out.' So why did you not obey God? Why did you grab all this loot? Why, with God's eyes on you all the time, did you brazenly carry out this evil?"
20-21Saul defended himself. "What are you talking about? I did obey God. I did the job God set for me. I brought in King Agag and destroyed the Amalekites under the terms of the holy ban. So the soldiers saved back a few choice sheep and cattle from the holy ban for sacrifice to God at Gilgal—what's wrong with that?"