Yahya related to me from Malik from Ishaq ibn Abdullah ibn AbiTalha that Rafiibn Ishaq, a mawla of the family of ash-Shifa who wasknown as the mawla of Abu Talha, heard Abu Ayyub al-Ansari, one of thecompanions of the Messenger of Allah, may Allah bless him and granthim peace, say, while he was in Egypt, "By Allah! I don't know how todeal with these lavatories." The Messenger of Allah, may Allah blesshim and grant him peace, said, "When you go to defecate or urinate, donot expose your genitals towards the qibla, and do not put your backto it."
USC-MSA web (English) reference: Book 14, Hadith 1
Arabic reference: Book 14, Hadith 458