Musannaf Ibn Abi Shayba 2:54

Abu Bakr narrated to us, he said: Hafs narrated to us, from Hajjaj, from ‘Ata’, from Abu Mahdhura and from Talha, from Suwayd, from Bilal, that they both would not perform the *tathwib* (the call "as-salatu khayrun min an-nawm") except in the dawn prayer.