Musannaf Ibn Abi Shayba 36:279

Abu Khalid al-Ahmar narrated to us, from Humayd, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) went out on a cold morning, while the Emigrants (Muhajirun) and the Helpers (Ansar) were digging the trench. When he looked at them, he said: "Indeed, the true life is the life of the Hereafter, so forgive the Ansar and the Muhajira." They answered him: "We are those who pledged allegiance to Muhammad, upon Jihad, for as long as we remain."