Deuteronomy 24:18-22

18Remember that you were slaves in Egypt and the Lord your God redeemed you from there. That is why I command you to do this. 19When you are harvesting in your field and you overlook a sheaf, do not go back to get it. Leave it for the foreigner, the fatherless and the widow, so that the Lord your God may bless you in all the work of your hands. 20When you beat the olives from your trees, do not go over the branches a second time. Leave what remains for the foreigner, the fatherless and the widow. 21When you harvest the grapes in your vineyard, do not go over the vines again. Leave what remains for the foreigner, the fatherless and the widow. 22Remember that you were slaves in Egypt. That is why I command you to do this.