1. There are great rewards in store in the Hereafter for those who call out the azaan.
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال لو يعلم الناس ما في النداء والصف الأول ثم لم يجدوا إلا أن يستهموا عليه لاستهموا (صحيح البخاري، الرقم: 615)
Hazrat Abu Hurairah (radhiyallahu anhu) reports that Hazrat Rasulullah (sallallahu alaihi wasallam) said, “If the people only know the great reward for calling out the azaan and performing salaah in the first saff, and thereafter they could find no alternative to decide who would be granted that honour besides drawing lots, they would definitely draw lots to decide.”
2. Every creation (whether jinn, human or any other creation) that hears the voice of the muazzin calling out the azaan will testify on his behalf on the Day of Qiyaamah.
عن عبد الرحمن بن عبد الله بن عبد الرحمن بن أبي صعصعة الأنصاري ثم المازني عن أبيه أنه أخبره أن أبا سعيد الخدري رضي الله عنه قال له إني أراك تحب الغنم والبادية فإذا كنت في غنمك أو باديتك فأذنت بالصلاة فارفع صوتك بالنداء فإنه لا يسمع مدى صوت المؤذن جن ولا إنس ولا شيء إلا شهد له يوم القيامة قال أبو سعيد سمعته من رسول الله صلى الله عليه وسلم (صحيح البخاري، الرقم: 609)
It is reported regarding Hazrat Abdullah bin Abdir Rahmaan bin Abi Sa’sa’ah (radhiyallahu anhu) that on one occasion, Hazrat Abu Sa’eed Khudri (radhiyallahu anhu) said to him, “I see that you like to remain with your livestock (grazing them) in the open fields. When you are among your livestock or in the open fields, (and the time of salaah enters) and you wish to call out the azaan, then you should raise your voice and call out the azaan, for certainly the jinn, humans or any other creation that hears the voice of the muazzin as far as it reaches will testify on his behalf on the Day of Qiyaamah.” Hazrat Abu Sa’eed (radhiyallahu anhu) said, “I heard this from Rasulullah (sallallahu alaihi wasallam).”