One-fifth of Booty to the Cause of Allah (Khumus)

Bukhari :: Book 4 :: Volume 53 :: Hadith 377

Narrated Anas bin Malik:

While I was walking with the Prophet who was wearing a Najrani outer garment with a thick hem, a bedouin came upon the Prophet and pulled his garment so violently that I could recognize the impress of the hem of the garment on his shoulder, caused by the violence of his pull. Then the bedouin said, "Order for me something from Allah's Fortune which you have." The Prophet turned to him and smiled, and ordered that a gift be given to him.