Abu Dawud
Tributes, Spoils And Rulership
Book Number: 013 / Hadith Number: 3040
Narated By 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 (pbuh) said: Tithes are to be levied on Jews and Christians, but not on Muslims.