It was narrated that Ma'qil bin Abu Ma'qil Al-Asadi, who was a Companion of the Prophet, said:
"The Messenger of Allah forbade us from facing either of the two Qiblah when defecating or urinating." (FR)
English reference (FR): Vol. 1, Book 1, Hadith 319 (FR)
Arabic reference (FR): Book 1, Hadith 340 (FR)