Musnad Ahmad 788:20

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Qatadah, from Yunus ibn Jubayr, from Hattan ibn 'Abd Allah al-Raqashi, that Abu Musa al-Ash'ari led his companions in prayer, and he mentioned the hadith. He said: The Messenger of Allah (peace and blessings of Allah be upon him) delivered a sermon to us, and he clarified our Sunnah for us and taught us our prayer. He said: "When you pray, straighten your rows, then let one of you lead you." And he mentioned the rest of the hadith.