Musannaf Ibn Abi Shayba 2:50

Abu Bakr narrated to us, he said: Abu Khalid al-Ahmar narrated to us, from Hajjaj, from ‘Ata’, from Abu Mahdhura, that he used to perform the Adhan for the Messenger of Allah (ﷺ), and for Abu Bakr, and for ‘Umar. And there was in his Adhan: "Prayer is better than sleep."