Sahih Bukhari Volume 4, Book 56, Hadith Number 772.

Narated By Anas : A bowl of water was brought to the Prophet while he was at Az-Zawra. He placed his hand in it and the water started flowing among his fingers. All the people performed ablution (with that water). Qatada asked Anas, “How many people were you?” Anas replied, “Three hundred or nearly three-hundred.”