Musnad Ahmad 32:1248

Sulayman narrated to us, Shu'bah narrated to us, from Mu'awiyah ibn Qurrah, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) said while they were digging the trench: "O Allah, there is no good except the good of the Hereafter, so rectify the Ansar and the Muhajirun."