It was narrated from Jabir bin 'Abdullah:
"Abu Sa'eed Al-Khudri narrated to me, that he bears witness that the Messenger of Allah forbade facing the Qiblah when defecating or urinating.'" (RU)
English reference (RU): Vol. 1, Book 1, Hadith 320 (RU)
Arabic reference (RU): Book 1, Hadith 341 (RU)