Abu Dawud Book 14, Hadith Number 3206.

Narated By Al-Bara’ ibn Azib : We went out with the Apostle of Allah (PBUH) to the funeral of a man of the Ansar, but when we reached the grave, the niche in the side had not yet been made, so the Prophet (PBUH) sat down facing the qiblah, and we sat down along with him.