Musannaf Ibn Abi Shaybah 38743 — the first to do a thing, and who did

Tawus said: Tathwib in the Fajr adhan was first begun by Sayyiduna Bilal (may Allah be pleased with him) in the time of Sayyiduna Abu Bakr (may Allah be pleased with him). After saying 'Hayya ala al-falah' he would say twice: 'As-salatu khayrun min an-nawm' (Prayer is better than sleep).