Musannaf Ibn Abi Shaybah

Hazrat Abu Juhaifa narrates that Hazrat Bilal planted a spear, then gave the call to prayer (adhan) in such a way that he placed his fingers in his ears.

Hazrat Ibn Sirin says that the muezzin will face the qiblah and place his fingers in his ears.

Hazrat Naseer said that I saw Hazrat Ibn Umar (may Allah be pleased with them) giving the call to prayer while sitting on a camel. Hazrat Sufyan asked Naseer whether he had placed his fingers in his ears; he replied, no.

Muhammad says that the call to prayer (adhan) is that a person should say "Allahu Akbar, Allahu Akbar" and then place his fingers in his ears. Ibn al-Asam was the first to abandon the practice of placing fingers in the ears.

Hazrat Hisham states that when Hazrat Ibn Sirin would give the adhan, he would leave his hands open, then when he reached "Hayya 'ala-s-Salah" and "Hayya 'ala-l-Falah," he would insert his fingers into his ears.