Musannaf Ibn Abi Shayba 13:1481

Abu Bakr narrated to us, he said: Abu al-Ahwas narrated to us, from Simak, from Ikrimah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not face the Qiblah (while relieving yourselves), do not gather (to bid up prices), and let not some of you outbid others."