Sayyiduna al-Sa'ib bin Yazid (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) had only one mu'adhdhin; no one other than him gave the adhan for him (peace and blessings be upon him). When the Messenger of Allah (peace and blessings be upon him) sat on the pulpit on Friday, he would give the adhan at the door of the mosque, and when he (peace and blessings be upon him) came down, the iqamah would be called. Then it remained the same in the time of Sayyiduna Abu Bakr (may Allah be pleased with him), and then it remained the same in the time of Sayyiduna Umar (may Allah be pleased with him), until, when the time of Sayyiduna Uthman (may Allah be pleased with him) came and the people had increased, he began to have the first adhan called in the market, on a house of his called "al-Zawra'". The adhan would be given on it, and then when Sayyiduna Uthman (may Allah be pleased with him) sat on the pulpit, his first mu'adhdhin would give the adhan, and when he came down, the iqamah would be called.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6612