A man from the Ansar narrates from his father: The Prophet (peace and blessings be upon him) forbade that we should face either of the two qiblahs while urinating or defecating.
Imam Ahmad recorded it; its chain contains a narrator who has not been named.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1009