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.'" (ID)
English reference (ID): Vol. 1, Book 1, Hadith 320 (ID)
Arabic reference (ID): Book 1, Hadith 341 (ID)