Musannaf Ibn Abi Shayba 13:445

Abu Bakr narrated to us, he said: Hukām al-Rāzī narrated to us, from al-Muthannā, from ‘Aṭā’, that he used to see no harm in that. He said: And Ṭāwūs used to dislike it, unless it was for a known wage.