It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) forbade walking in one sandal or one khuff, spending the night alone in a house, and relieving oneself in open ground without any cover, unless one bends down, or, if one encounters an enemy, moves oneself aside.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12307