Tribute, Spoils, and Rulership (Kitab Al-Kharaj, Wal-Fai' Wal-Imarah)
Dawud :: Book 19 : Hadith 3040
Narrated Ubaydullah:
Harb ibn Ubaydullah told on the authority of his grandfather, his mother's father, that he had it on the authority of his father that the Apostle of Allah (peace_be_upon_him) said: Tithes are to be levied on Jews and Christians, but not on Muslims.