Sahih Bukhari Volume 5, Book 57, Hadith Number 74.

Narated By Qais : I heard Sad saying, “I was the first amongst the ‘Arabs who shot an arrow for Allah’s Cause. We used to fight along with the Prophets, while we had nothing to eat except the leaves of trees so that one’s excrete would look like the excrete balls of camel or a sheep, containing nothing to mix them together. Today Banu Asad tribe blame me for not having understood Islam. I would be a loser if my deeds were in vain.” Those people complained about Sad to ‘Umar, claiming that he did not offer his prayers perfectly.