1 Samuel 15:3

Now go and smite Amalek
This was one of the three things the Israelites were obliged to do when they came into the land of Canaan, as Kimchi observes; one was, to appoint a king over them, another, to build the house of the sanctuary, and the third, to blot out the name and memory of Amalek, see ( Deuteronomy 25:19 ) and this work was reserved for Saul, their first king:

and utterly destroy all that they have, and spare them not;
all were to be devoted to destruction, and nothing remain to be made use of in any way, to any profit and advantage; living creatures were to be put to death, and everything else burnt and destroyed:

but slay both men and women, infant and suckling;
neither sex nor age were to be regarded, no mercy and pity shown to any; they had shown none to Israel when weak and feeble, and by the law of retaliation none was to be exercised on them:

ox and sheep, camel and ass;
though useful creatures, yet not to be spared; as not men, women, and children, through commiseration, so neither these through covetousness, and neither of them on any pretence whatsoever. Children suffered for their parents, and cattle because of their owners, and both were a punishment to their proprietors; an ox, or any other creature, might not be spared, lest it should be said, as Kimchi observes, this was the spoil of Amalek, and so the name and memory of Amalek would not be blotted out.