Samuel also said unto Saul, “The LORD sent me to anoint thee to be king over his people, over Israel: now therefore hearken thou unto the voice of the words of the LORD. ‘Thus saith the LORD of hosts, I remember that which Amalek did to Israel, how he laid wait for him in the way, when he came up from Egypt. Now 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 gathered the people together, and numbered them in Telaim, two hundred thousand footmen, and ten thousand men of Judah. And Saul came to a city of Amalek, and laid wait in the valley. And Saul said unto the Kenites, “Go, depart, get you down from among the Amalekites, lest I destroy you with them: for ye shewed kindness to all the children of Israel, when they came up out of Egypt.” So the Kenites departed from among the Amalekites. And Saul smote the Amalekites from Havilah until thou comest to Shur, that is over against Egypt. And he took Agag the king of the Amalekites alive, 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.” And it grieved Samuel; and he cried unto the LORD all night. 1 Samuel 15:1-11
References: 1 Samuel 15:12-35; 13; 14; Esther 3:1; Isaiah 14:21-22; Jonah 3:10; 4:2; Luke 19:41-44; Romans 8:20-22; 9:1-3