Sahih Bukhari Volume 7, Book 63, Hadith Number 216A.

Narrated By Abu Huraira : Abul Qasim (the Prophet) said, “There is an hour (or a moment) of particular significance on Friday. If it happens that a Muslim is offering a prayer and invoking Allah for some good at that very moment, Allah will grant him his request.” (The sub-narrator placed the top of his finger on the palm of the other hand between the middle finger and the little one.)