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

Bukhari :: Book 4 :: Volume 53 :: Hadith 374

Narrated Anas:

The Prophet said, "I give to Quraish people in order to let them adhere to Islam, for they are near to their life of Ignorance (i.e. they have newly embraced Islam and it is still not strong in their hearts."