Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "I am the Prophet, this is no lie; and I am the son of Abd al-Muttalib. I am the most eloquent of the Arabs. I was born among Banu Quraysh and I was raised among Banu Sa'd bin Bakr, so how could any faulty speech (lahn) come to me?"
At-Tabarani recorded it; its chain contains Mubashshir bin Ubayd, who is matruk (abandoned).