In the book of 1 Samuel (15:3), God said to Saul:
“Now go, attack the Amalekites, and totally destroy all that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels and donkeys.”
Saul dutifully exterminated the women, the children, the babies and all of the men – but then he spared the king. He also saved some of the tastier looking calves and lambs. God was furious with him for his failure to finish the job.