(3) باب السُّنَّةِ فِي الأَذَانِ
It was narrated that 'Uthman bin Abul-As said:
"The last instruction that the Messenger of Allah gave to me was that I should not appoint a Mu'adh-dhin who took payment for the Adhan." (sahih)
Reference: Sunan Ibn Majah 714
In-book reference: Book 3, Hadith 9
English translation: Vol. 1, Book 3, Hadith 714