We were laying siege to the fortress of Khaybar when someone threw down a sack containing fat. I leapt forward to grab it, then turned and saw the Prophet ﷺ, so I felt embarrassed before him.In another wording, On the day of Khaybar, I obtained a sack of fat. I clutched it and said to myself, "I will not give any of this to anyone today." Then I turned and saw the Messenger of Allah ﷺ smiling.
كنا محاصرين قصر خيبر فرمي إنسان بجراب فيه شحم، فنزوت لأخذه فالتفت فإذا النبي ﷺ فاستحييت منه. وفي لفظ: أصبت جرابا من شحم يوم خيبر قال: فالتزمته فقلت: لا أعطي اليوم أحدا من هذا شيئا، قال: فالتفت فإذا رسول الله ﷺ متبسما.
Bukhari reported it in the chapter on the obligation of the khumus (3153), and Muslim in jihad and expeditions (1772: 73), both through the route of Shubah, who said, Humayd bin Hilal narrated to me, I heard Abdullah bin Mughafal, and he mentioned it. The other wording is Muslim's (1772: 72), through the route of Sulayman bin Mughira, who said, Humayd bin Hilal narrated to us with it, and he mentioned it.