Musnad Ahmad 1060:82

Sufyan narrated to us, from al-Zuhri, from ‘Ata’ ibn Yazid al-Laythi, who said: I heard Abu Ayyub informing about the Prophet, may Allah bless him and grant him peace, who said: "Do not face the Qibla when defecating or urinating, but face the east or the west." Abu Ayyub said: "Then we arrived in Ash-Sham and found latrines that had been built facing the Qibla, so we would turn aside and ask Allah for forgiveness."