Deuteronomy 23:12 – 14
New International Version (NIV1984)
12 Designate a place outside the camp where you can go to relieve yourself. 13 As part of your equipment have something to dig with, and when you relieve yourself, dig a hole and cover up your excrement. 14 For the Lord your God moves about in your camp to protect you and to deliver your enemies to you. Your camp must be holy, so that he will not see among you anything indecent and turn away from you.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=Deuteronomy 23:12 –14&version=NIV1984