Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.095A.
Many hadith describe the virtues of the azhan and the one who calls it. Such hadith include the following:
Abu Hurairah reported that the Prophet said, “If the people knew what was in the azhan and the first row (of the prayer in virtue), and that they could not get it save by drawing lots, they would draw lots. If they knew the reward for praying the noon prayer early in its time, they would race to it. And if they knew the reward for the night and the morning prayers in congregation, they would come to them even if they had to crawl.” (Related by al-Bukhari and others.)
Mu’awiyyah reported that the Prophet, upon whom be peace, said, “The callers to prayer will have the longest necks of all people on the Day of Resurrection.” (Related by Ahmad, Muslim, and Ibn Majah.)
Al-Barra’ ibn ‘Aazib reported that the Prophet, upon whom be peace, said, “Allah and His angels pray upon those in the first rows. And the caller to prayer is forgiven, for as far as his voice reaches and whoever hears him will confirm what he says. He will get a reward similar to those who pray with him.” This hadith is related by Ahmad and an-Nasa’i. Al-Munzhiri says its chain is good.
Abu ad-Darda’ reported that he heard the Prophet, upon whom be peace, say, “If three people do not make the azhan and establish the prayer among themselves, Satan gains mastery over them.” (Related by Ahmad.)
Abu Hurairah reported that the Prophet, upon whom be peace, said, “The imam is a guarantor, and the caller to prayer is one who is given the trust. O Allah, guide the imam and forgive the caller to prayer.”
‘Uqbah ibn ‘Aamar said he heard the Prophet, upon whom be peace, say, “Your Lord, the Exalted, is amazed (and pleased) by one who is watching sheep in his pasture, then goes to the mountain to make the call to prayer and pray. Allah, the Exalted, says, ‘Look at my slave there who makes the call to prayer and establishes the prayer out of fear of Me. I have forgiven my slave and have allowed him to enter Paradise.”‘ (Related by Ahmad, Abu Dawud and anNasa’i.)