It is narrated from al-Hasan (al-Basri) (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) said: "The muezzins are the trustees of the Muslims over their prayers and their needs."
It has also been narrated from Yunus, from al-Hasan, from Jabir, but that is not mahfuz (preserved).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2031