Deut 23:20-21

20On loans to a foreigner you may charge interest, but on loans to another Israelite you may not charge interest, so that the Lord your God may bless you in all your undertakings in the land that you are about to enter and possess.21If you make a vow to the Lord your God, do not postpone fulfilling it; for the Lord your God will surely require it of you, and you would incur guilt.