Musnad Ahmad 33:755

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Aban ibn Salih narrated to me, from Mujahid ibn Jabr, from Jabir ibn Abdullah al-Ansari, who said: "The Messenger of Allah, peace and blessings of Allah be upon him, had forbidden us from turning our backs to the Qibla, or facing it with our private parts when we urinated." He said: "Then I saw him, a year before his death, urinating while facing the Qibla."