Abu Dawud Book 13, Hadith Number 3043.

Narated By A man of Banu Taghlib : Harb ibn Ubaydullah ibn Umayr ath-Thaqafi told on the authority of his grandfather, a man of Banu Taghlib: I came to the Prophet (PBUH), embraced Islam, and he taught me Islam. He also taught me how I should take sadaqah from my people who had become Muslim. I then returned to him and said: Apostle of Allah, I remembered whatever you taught me except the sadaqah. Should I levy tithe on them? He replied: No, tithes are to be levied on Christians and Jews.