Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 750
Yahya narrated it on the authority of his uncle that he had been sitting in the company of Mu'awiya b. Abu Sufyan when the Mu'adhdhin called (Muslims) to prayer. Mu'awiya said: I heard the Messenger of Allah (may peace be upon him) saying The Mu'adhdhins will have the longest necks on the Day of Resurrection.