Musnad Ahmad 32:1184

Ibn Abi ‘Adi narrated to us, from Humayd, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) went out while the Emigrants (Muhajirun) were digging the trench on a cold morning. Anas said: They had no servants. The Messenger of Allah (may Allah bless him and grant him peace) said: "O Allah, indeed the true life is the life of the Hereafter, so forgive the Helpers (Ansar) and the Emigrants." He said: So they answered him: We are those who pledged allegiance to Muhammad, To strive (Jihad) as long as we remain forever. Or: We shall not flee.