(a) It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Only one who has ablution should give the adhan."
(b) It is narrated from al-Zuhri that Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: Only one who has ablution should call the adhan for the prayer.
Mu'awiyah bin Yahya al-Sadafi, who narrated it in this way (as the Prophet's words), is da'if (weak); the correct version is the narration of Yunus bin Yazid al-Ayli and others from al-Zuhri, as the words of Abu Hurayrah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1858