Jami` at-Tirmidhi 209
جامع الترمذي#209SahihUthman bin Abi Al-As narrated:"Indeed, amount the last (of orders) Allah's Messenger ordered me with was to employ a Mu'adh-dhin who would not take a wage for his Adhan
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 2:61