Deuteronomy 23:13-14:
13) And you shall have a designated place outside the camp, so that you can go out there [to use it as a privy].
14) And you shall keep a stake in addition to your weapons; and it shall be, when you sit down outside [to relieve yourself], you shall dig with it, and you shall return and cover your excrement.

So literally, "Don't shit in the middle of camp and bury your shit when you're done for God's sake!"