Musnad Abu Ya'la al-Mawsili 54:8

Narrated to us Muhriz, narrated to us Rishdin ibn Sa'd, from Zabban ibn Fa'id, from Sahl ibn Mu'adh, from his father, from the Prophet (may Allah bless him and grant him peace), who said: "Whoever guards behind the Muslims in the way of Allah, as a volunteer, not being taken by a ruler, will not see the Fire with his eye, except for the fulfillment of the oath. For Allah, glory be to Him, who has no partner, says: 'And there is none of you except he will come to it' (Maryam: 71)."