(17) باب كَيْفَ كَانَ عَيْشُ النَّبِيِّ صلى الله عليه وسلم وَأَصْحَابِهِ، وَتَخَلِّيهِمْ مِنَ الدُّنْيَا
Narrated Sa`d:
I was the first man among the Arabs to throw an arrow for Allah's Cause. We used to fight in Allah's Cause while we had nothing to eat except the leaves of the Hubla and the Sumur trees (desert trees) so that we discharged excrement like that of sheep (i.e. unmixed droppings). Today the (people of the) tribe of Bani Asad teach me the laws of Islam. If so, then I am lost, and all my efforts of that hard time had gone in vain.
Reference: Sahih al-Bukhari 6453
In-book reference: Book 81, Hadith 42
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 76, Hadith 460