(Pro 25:21 KJV) If thine enemy be hungry, give him bread to eat; and if he be thirsty, give him water to drink:
Clearly the NT writers were familiar with the Proverbs:
(Mat 5:44 KJV) But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
(Rom 12:20 KJV) Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head.
One of the bits of ignorance that amazes me is the people who think mercy and graciousness are limited to the NT. Jesus taught what the OT said. We do no study ourselves so we fall for the nonsense that the God of the OT is different than the God of the NT.
This is also why war waged by Christians is different than war raged by followers of other gods. We are commanded to love our enemies even when it is necessary for the government to use the sword to deal with evil. That limits our actions. The love of Christ that controls us is the same love that will sit on the judgment seat. It is the same love that condemned the man not dressed for the wedding. It is the same love that did not put up with the nonsense of the Pharisees. It is the same love that went to the cross and died in our place. Biblical love is not the same as the love of the movie screen or the romance novel. This is the love that we apply to our lives.