Unto a stranger thou mayest lend upon usury; but unto thy brother thou shalt not lend upon usury: that the LORD thy God may bless thee in all that thou settest thine hand to in the land whither thou goest to possess it.
You can lend money to someone you don't know with extra pay, but don't lend to your family like that. This is so God will bless everything you do in the land where you live.