Musannaf Ibn Abi Shayba 2:221

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from ‘Abbad ibn Ishaq, from Suhayl, from his father, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), he said: "O Allah, guide the Imams and forgive the Mu'adhdhins."