Musnad Abu Ya'la al-Mawsili 106:79

Muhammad narrated to us, Muhammad narrated to us, Shu'bah narrated to us, from Abu Ishaq, who said: I heard al-Bara' saying: When the Ansar performed Hajj, they would not enter houses except from their backs. A man from the Ansar came and entered through his door, and it was said to him regarding that. Then it was revealed: "And it is not righteousness to enter houses from their backs" [Al-Baqarah: 189], up to the end of the verse.