Musnad Ahmad 30:250

Sufyan narrated to us, from Ibn ‘Ajlan, from al-Qa‘qa‘ ibn Hakim, from Abu Salih, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him: "I am to you only like a father. When you come to relieve yourselves, do not face the Qiblah, nor turn your backs to it." And he forbade the use of dung and decayed bones, and that a man should clean himself with his right hand.