Musnad Ahmad 8:127

Yahya ibn Sa'id narrated to us, Isma'il narrated to us, Qays narrated to us, he said: I heard Sa'd ibn Malik saying: "I am indeed the first of the Arabs to shoot an arrow in the way of Allah. I have seen us raiding 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 *hublah* (a type of tree) and this *samur* (acacia). So much so that one of us would defecate just as a sheep defecates, having no mixture. Then, the tribe of Banu Asad began to rebuke me regarding the religion. If that were the case, I would have failed, and my deeds would have been lost."