Ibn Majah

´'Abdur-Rahman bin Sa'd bin 'Ammar bin Sa'd, who was the Mu'adh-dhin of the Messenger of Allah narrated from his grandfather, that:` The Messenger of Allah commanded Bilal to put his fingers in his ears when calling the Adhan, and he said: "It makes the voice louder."

´It was narrated from 'Awn bin Abu Juhaifah that his father said:` "I came to the Messenger of Allah in Abtah, when he was in a red tent. Bilal came out and gave the call to prayer, turning around and putting his fingers in his ears."

´It was narrated that Ibn 'Umar said:` "The Messenger of Allah said: There are two characteristics in which the Muslims are dependent upon their Mu'adh-dhins: their prayer and their fasting."

´It was narrated that Jabir bin Samurah said:` "Bilal did not delay the Adhan from its proper time, but he sometimes delayed the Iqamah a little."

´It was narrated that 'Uthman bin Abul-As said:` "The last instruction that the Messenger of Allah gave to me was that I should not appoint a Mu'adh-dhin who took payment for the Adhan." (sahih)

´It was narrated that Bilal said:` "The Messenger of Allah commanded me (with Tathwib) in the Adhan for Fajr, and he forbade me to do so in the Adhan for 'Isha'."

´It was narrated that Bilal came to the Prophet to call him for the Fajr prayer, and was told:` "He is sleeping." He said: "As-salatu khairum minan-nawm, As-salatu khairum minan-nawm (The prayer is better than sleep, the prayer is better than sleep). These words were approved of in the Adhan for the Fajr, and that is how it remained.

´It was narrated that Ziyad bin Harith As-Suda'i said:` "I was with the Messenger of Allah on a journey, and he commanded me to call the Adhan. Bilal wanted to call the Iqamah, but the Messenger of Allah said: 'The brother of Suda' called the Adhan, and the one who calls the Adhan is the one who calls the Iqamah.'"