Sahih Bukhari Volume 008, Book 075, Hadith Number 409.

Narated By Abu Huraira : Abu-l-Qasim (the Prophet) said, "On Friday there is a particular time. If a Muslim happens to be praying and invoking Allah for something good during that time, Allah will surely fulfill his request." The Prophet pointed out with his hand. We thought that he wanted to illustrate how short that time was.