Musnad Ahmad 482:63

Yazid narrated to us, Muhammad ibn Ishaq informed us, from Yazid ibn Abi Habib, from Abd al-Rahman ibn Shumasah, who said: I heard Uqbah ibn Amir al-Juhani saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The collector of illegal taxes (sahib maks) shall not enter Paradise." Meaning the tithe-collector (al-ashshar).