Musnad Ahmad 32:1956

Waki’ narrated to us, from Shu’bah, from Qatadah, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Straighten your rows, for indeed, from the excellence of the prayer is the straightening of the row." Abu Qatan narrated to us, he said: I heard Shu’bah saying, regarding Qatadah: "Did he attribute it to the Prophet (marfu’)?" I thought he meant the hadith, so Abdullah ibn Uthman said to me: "This is one of them."