Sahih Bukhari Volume 4, Book 56, Hadith Number 768.

Narated By ‘Aisha : The Prophet used to talk so clearly that if somebody wanted to count the number of his words, he could do so.

Narrated Urwa bin Az-Zubair: ‘Aisha said (to me), “Don’t you wonder at Abu so-and-so who came and sat by my dwelling and started relating the traditions of Allah’s Apostle intending to let me hear that, while I was performing an optional prayer. He left before I finished my optional prayer. Had I found him still there. I would have said to him, ‘Allah’s Apostle never talked so quickly and vaguely as you do.'”