1. Freedom from the fire of Jahannum is promised for the one who calls out the azaan for seven years.
عن ابن عباس رضي الله عنهما أن النبي صلى الله عليه وسلم قال من أذن سبع سنين محتسبا كتبت له براءة من النار (سنن الترمذي، الرقم: 206)
Hazrat Ibnu Abbaas (radhiyallahu anhuma) reports that Hazrat Rasulullah (sallallahu alaihi wasallam) said, “The one who calls out the azaan for seven years with sincerity and the hope of attaining reward receives the guarantee of freedom from the fire of Jahannum.”
2. Hazrat Rasulullah (sallallahu alaihi wasallam) made dua for the forgiveness of those who call out the azaan.
عن أبى هريرة رضي الله عنه قال قال رسول الله صلى الله عليه وسلم الإمام ضامن والمؤذن مؤتمن اللهم أرشد الأئمة واغفر للمؤذنين (سنن أبي داود، الرقم: 517)
Hazrat Abu Hurairah (radhiyallahu anhu) reports that Hazrat Rasulullah (sallallahu alaihi wasallam) said, “The imaam is responsible (for the salaah of the entire congregation) and the muazzin is one who is entrusted with a trust (i.e. he has been entrusted with the duty of calling out the azaan on its prescribed time). O Allah Ta’ala, guide the imaams (towards fulfilling their obligation of leading the salaah correctly) and forgive the muazzins (for their shortcomings).”