Musannaf Ibn Abi Shaybah

Hazrat Imran bin Abi Al-Ja'd narrates that Hazrat Aswad bin Yazid heard the muezzin say these words in the Fajr adhan: "As-salatu khayrun minan-nawm" (Prayer is better than sleep). So he said that do not add to the adhan those words which are not a part of it.