Musnad Ahmad 8:179

Yazid ibn Harun narrated to us, Ismail informed us, from Qays, who said: I heard Sa’d ibn Malik saying: "By Allah, I am the first of the Arabs to have shot an arrow in the way of Allah. We used to go on expeditions with the Messenger of Allah, may Allah bless him and grant him peace, and we had no food to eat except the leaves of the *hubla* (a type of tree) and this *samur* (acacia), to the point that one of us would defecate just as a sheep defecates, having no mixture in it. Then, the Banu Asad have come to rebuke me regarding the religion. If that were the case, I would have failed, and my deeds would have been lost."