Musnad Ahmad 554:3

'Affan narrated to us, he said: Wuhayb narrated to us, he said: 'Amr ibn Yahya narrated to us, from Abu Zayd, from Ma'qil ibn Abi Ma'qil al-Asadi, who said: "The Messenger of Allah (may Allah bless him and grant him peace) forbade that the two qiblas be faced while relieving oneself or urinating."