Musnad Ahmad 1013:20

Qutaybah ibn Sa'id narrated to us, 'Abd al-'Aziz ibn Abi Hazim narrated to us, from his father, from Sahl ibn Sa'd, who said: We were with the Messenger of Allah, may Allah bless him and grant him peace, at the Trench while they were digging, and we were carrying the dirt on our shoulders. The Messenger of Allah, may Allah bless him and grant him peace, said: "O Allah, there is no life except the life of the Hereafter, so forgive the Emigrants and the Helpers."