Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) said: One day the Messenger of Allah (peace and blessings be upon him) led the prayer while the people were behind him, and while he (peace and blessings be upon him) was praying, he kept moving backwards in that same state.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5812