Musannaf Ibn Abi Shaybah 2177 — Those who said in the adhan: Prayer

Suwayd bin Ghafalah sent this message to his muezzin: When you reach 'Hayya 'ala al-falah' (come to success), say 'al-salatu khayrun min al-nawm (prayer is better than sleep)', for that was the adhan of Sayyiduna Bilal (may Allah be pleased with him).