Saul said, Bring hither a burnt offering to me, and peace offerings. And he offered the burnt offering.
And Samuel said to Saul, Thou hast done foolishly: thou hast not kept the commandment of the LORD thy God ... But now thy kingdom shall not continue. 1 Samuel 13:9, 13-14
Thus saith the LORD of hosts ... go and smite Amalek, and utterly destroy all that they have, and spare them not; but slay both man and woman, infant and suckling, ox and sheep, camel and ass.
And Saul smote the Amalekites ... and utterly destroyed all the people with the edge of the sword. But Saul and the people spared Agag, and the best of the sheep, and of the oxen, and of the fatlings, and the lambs, and all that was good, and would not utterly destroy them: but every thing that was vile and refuse, that they destroyed utterly.
Then came the word of the LORD unto Samuel, saying, It repenteth me that I have set up Saul to be king: for he is turned back from following me, and hath not performed my commandments. 1 Samuel 15:2-3, 7-11