Yahya related to me from Malik from Ayyub ibn Abi Tamima as-Sakhtayani that Umar ibn Abd al-Aziz, when writing about wealth thatone of his governors had collected unjustly, ordered it to be returnedto its owner and zakat to be taken from it for the years that hadpassed. Then shortly afterwards he revised his order with a messagethat zakat should only be taken from it once, since it was not wealthin hand.
USC-MSA web (English) reference: Book 17, Hadith 18
Arabic reference: Book 17, Hadith 597