Sahih Muslim Book 4, Hadith Number 750.

Chapter : He who hears the Adhin should respond like it, invoke blessings upon the Apostle (may peace be upon him)and then beg for him the Wasila.

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.