Musannaf Ibn Abi Shayba 2:105

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 (may Allah bless him and grant him peace), and for Abu Bakr and Umar. He would not perform the Adhan until the dawn appeared.