1 Samuel 15:14-18

And Samuel said, What meaneth then this bleating of the sheep in mine ears, and the lowing of the oxen which I hear?

And Saul said, They have brought them from the Amalekites: for the people spared the best of the sheep and of the oxen, to sacrifice unto the LORD thy God; and the rest we have utterly destroyed.

Then Samuel said unto Saul, Stay, and I will tell thee what the LORD hath said to me this night. And he said unto him, Say on.

And Samuel said, When thou wast little in thine own sight, wast thou not made the head of the tribes of Israel, and the LORD anointed thee king over Israel?

And the LORD sent thee on a journey, and said, Go and utterly destroy the sinners the Amalekites, and fight against them until they be consumed.