Deuteronomy 23:9-11

American Standard Version

⁹ When thou goest forth in camp against thine enemies, then thou shalt keep thee from every evil thing. ¹⁰ If there be among you any man, that is not clean by reason of that which chanceth him by night, then shall he go abroad out of the camp, he shall not come within the camp: ¹¹ but it shall be, when evening cometh on, he shall bathe himself in water; and when the sun is down, he shall come within the camp.