Musannaf Ibn Abi Shayba 27:733

Abu Khalid narrated to us, from Humayd, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) 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 Helpers and the Emigrants." They replied: "We are those who pledged allegiance to Muhammad to strive (Jihad) for as long as we remain."