Deuteronomy 23:12-14

Let there be a place outside the tent-circle to which you may go; And have among your arms a spade; and when you have been to that place, let that which comes from you be covered up with earth: For the Lord your God is walking among your tents, to keep you safe and to give up into your hands those who are fighting against you; then let your tents be holy, so that he may see no unclean thing among you, and be turned away from you.