Sa'd bin Abi Waqqias Radiyallahu 'Anhu reports that from the ummah of Muhammad Sallallahu 'Alayhi Wasallam I was the first to take the blood of a non-believer, and I was the first to shoot an arrow in the path of Allah.We (the group of Sahaabah in the early period of Islaam) went for jihaad in such a state, where we had nothing to eat. We ate the leaves of tree and pods of the acacia tree. As a result our jaw became ulcerous and wounded, and because of the leaves our excreta was like that of sheep and camel. After that too the people of Banu Asad threatened me. If the status of my ignorance in the deen is such as these people claim, then this world and the hereafter is lost. (The days in this world have been spent in poverty and difficulty, and the state of the deen is this that I do not have knowledge of salaah too).
English reference: Book 50, Hadith 355
Arabic reference: Book 52, Hadith 373