Musnad Ahmad 1060:80

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from 'Ata' ibn Yazid al-Laythi, from Abu Ayyub al-Ansari, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you goes to relieve himself, let him not face the Qibla nor turn his back to it, but let him face the east or the west." Abu Ayyub said: "When we arrived in Syria, we found latrines that had been built facing the Qibla, so we would turn aside and ask Allah for forgiveness."