Language:
كتاب فرض الخمس
57  
One-fifth of Booty to the Cause of Allah (Khumus)
(20)
Chapter: The food gained as war booty in the battlefield
(20)
باب مَا يُصِيبُ مِنَ الطَّعَامِ فِي أَرْضِ الْحَرْبِ
Sahih al-Bukhari 3153

Narrated `Abdullah bin Mughaffal:

While we were besieging the fort of Khaibar, a person threw a leather container containing fat, and I ran to take it, but when I turned I saw the Prophet (standing behind), so I felt embarrassed in front of him.

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ حُمَيْدِ بْنِ هِلاَلٍ، عَنْ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ ـ رضى الله عنه ـ قَالَ كُنَّا مُحَاصِرِينَ قَصْرَ خَيْبَرَ، فَرَمَى إِنْسَانٌ بِجِرَابٍ فِيهِ شَحْمٌ، فَنَزَوْتُ لآخُذَهُ، فَالْتَفَتُّ فَإِذَا النَّبِيُّ صلى الله عليه وسلم فَاسْتَحْيَيْتُ مِنْهُ‏.‏
Reference : Sahih al-Bukhari 3153
In-book reference : Book 57, Hadith 61
USC-MSA web (English) reference : Vol. 4, Book 53, Hadith 381
  (deprecated numbering scheme)