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