Musnad Ahmad 1153:2009

Yazid narrated to us, Hammad ibn Salamah informed us, from Khalid al-Hadhdha’, from Khalid ibn Abi al-Salt, who said: We were with Umar ibn Abd al-Aziz, and they mentioned a man sitting in the privy while facing the Qiblah, and they disliked that. Then he narrated from ‘Arak ibn Malik, from ‘Aishah, that this was mentioned in the presence of the Prophet, peace and blessings of Allah be upon him, and he said: "Have they really done it? Turn my seat towards the Qiblah."