1 Samuel 30:23-25

23David said, “You must not do so, my brothers, with what the Lord has given us. He has kept us safe and has handed over to us the band [of Amalekites] that came against us.

24And who will listen to you in regard to this matter? For as is the share of him who goes down into the battle, so shall his share be who stays by the provisions and supplies; they shall share alike.”

25So from that day forward he made it a statute and an ordinance for Israel to this day.