Deuteronomy 23:20-21

23:20 You may lend with interest to a foreigner, but not to your fellow Israelite; if you keep this command the Lord your God will bless you in all you undertake in the land you are about to enter to possess. 23:21 When you make a vow to the Lord your God you must not delay in fulfilling it, for otherwise he will surely hold you accountable as a sinner.