Musnad Abu Ya'la al-Mawsili 150:58

Muhammad ibn Abdullah narrated to us, Abdullah ibn Yazid narrated to us, Haywah narrated to us, Nafi’ ibn Sulayman narrated to me that Muhammad ibn Abi Salih informed him, from his father, that he heard Aisha, the wife of the Prophet, may Allah bless him and grant him peace, saying: The Messenger of Allah, may Allah bless him and grant him peace, said: "The Imam is a guarantor, and the Mu'adhdhin is a trustee. So may Allah guide the Imams and pardon the Mu'adhdhins."