Shama'il at-Tirmidhi 5

“I am the first man who shed blood in the cause of Allah (Almighty and Glorious is He), and I am the first man who shot an arrow in Allah’s cause. I had seen myself going forth to war in the troop of the Companions of Muhammad (blessing and peace be upon him). We ate nothing but tree-leaves and a kind of bean-fruit until the corners of our mouths were covered with ulcers, and one of us would excrete as the sheep and the camel excrete. The Banu Asad started instructing me in the religion. I had therefore failed and lost my way, and my work had come to naught.”