Musnad Ahmad 32:907

Waki’ narrated to us, Hammad bin Salamah narrated to us, from Abu al-Tayyah al-Dab’i, from Anas bin Malik, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying—while he was handing [materials] to his companions as they were building the mosque: "Behold, the [true] life is the life of the Hereafter, so forgive the Ansar and the Muhajirah."