Musnad Abu Ya'la al-Mawsili 1:124

Abu al-Rabi' al-Zahrani narrated to us, Hammad narrated to us, Ayyub narrated to us, he said: We saw with Thumamah ibn Abd Allah ibn Anas a document that Abu Bakr al-Siddiq wrote for Anas ibn Malik when he sent him to collect the Zakat of Bahrain, upon which was the seal of the Prophet, may Allah bless him and grant him peace, in which was [written] the like of this statement.