من لا يحضره الفقيه, volume 1, page 284

Hadith.873 - Al-Hasan ibn al-Sari reported from Imam Jafar ibn Muhammad Al-Sadiq (as) that He said: "It is part of the Sunnah (tradition) for a person giving the adhan (call to prayer) to place his fingers in his ears."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.

Hadith.874 - Khalid ibn Najih narrated from Imam (as) that He said: "The adhan and the iqamah must be recited with firmness." In another narration, it states, "They must be delivered with a pause."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.

Hadith.875 – Zurarah narrated from Imam Muhammad ibn Ali Al-Baqir (as) that He said: "The adhan is not sufficient for you unless you hear it yourself or understand it. Clearly articulate the 'alif' and 'ha'." Send blessings upon the Prophet and his family (as) whenever you mention him or hear someone mention him, whether during the adhan or outside of it. The louder your voice, without straining yourself, the more people will hear, and your reward will be greater."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.

Hadith.876 - Muawiya ibn Wahb asked Imam Jafar ibn Muhammad Al-Sadiq (as) about the adhan (call to prayer). The Imam said: "Raise your voice and speak loudly when giving the adhan. When performing the iqamah (second call to prayer), use a slightly lower voice. Do not delay your adhan and iqamah except until the time for prayer has arrived, and recite the iqamah quickly (with fluidity)."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.