كتاب الزهد والرقائق
55  
The Book of Zuhd and Softening of Hearts
Sahih Muslim 2967 c

Khalid b. Umair reported:

I heard Uqba b. Ghazwan as saving: I found myself as the seventh amongst the seven who had been along with Allah's Messenger (ﷺ). We had nothing to eat but the leaves of hubla (a wild tree) until the corners of our mouths were injured.
وَحَدَّثَنَا أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ حَدَّثَنَا وَكِيعٌ، عَنْ قُرَّةَ بْنِ خَالِدٍ، عَنْ حُمَيْدِ، بْنِ هِلاَلٍ عَنْ خَالِدِ بْنِ عُمَيْرٍ، قَالَ سَمِعْتُ عُتْبَةَ بْنَ غَزْوَانَ، يَقُولُ لَقَدْ رَأَيْتُنِي سَابِعَ سَبْعَةٍ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم مَا طَعَامُنَا إِلاَّ وَرَقُ الْحُبْلَةِ حَتَّى قَرِحَتْ أَشْدَاقُنَا ‏.‏
Reference : Sahih Muslim 2967c
In-book reference : Book 55, Hadith 21
USC-MSA web (English) reference : Book 42, Hadith 7077
  (deprecated numbering scheme)