It is narrated from Sayyiduna Abu Ayyub (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you goes out to relieve himself, let him not face the qiblah nor turn his back to it, but let him face east or west."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3926