Musnad Ahmad 1060:39

Isma'il narrated to us, Ma'mar informed us, from al-Zuhri, from 'Ata' ibn Yazid, from Abu Ayyub, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you goes to the privy, let him not face the Qiblah, nor turn his back toward it, but let him face the east or the west." Abu Ayyub said: "When we came to Ash-Sham, we found toilets built facing the Qiblah, so we would turn aside and ask Allah the Almighty for forgiveness."