Sahih Bukhari Volume 5, Book 62, Hadith 3730

حَدَّثَنَا عَمْرُو بْنُ عَوْنٍ، حَدَّثَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ إِسْمَاعِيلَ، عَنْ قَيْسٍ، قَالَ سَمِعْتُ سَعْدًا ـ رضى الله عنه ـ يَقُولُ إِنِّي لأَوَّلُ الْعَرَبِ رَمَى بِسَهْمٍ فِي سَبِيلِ اللَّهِ، وَكُنَّا نَغْزُو مَعَ النَّبِيِّ صلى الله عليه وسلم وَمَا لَنَا طَعَامٌ إِلاَّ وَرَقُ الشَّجَرِ، حَتَّى إِنَّ أَحَدَنَا لَيَضَعُ كَمَا يَضَعُ الْبَعِيرُ أَوِ الشَّاةُ، مَا لَهُ خِلْطٌ، ثُمَّ أَصْبَحَتْ بَنُو أَسَدٍ تُعَزِّرُنِي عَلَى الإِسْلاَمِ، لَقَدْ خِبْتُ إِذًا وَضَلَّ عَمَلِي‏.‏ وَكَانُوا وَشَوْا بِهِ إِلَى عُمَرَ، قَالُوا لاَ يُحْسِنُ يُصَلِّي‏.‏

Narrated 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.