Maliks Muwatta Book 5, Hadith Number 16.
Section : The Special Time in the Day of Jumua.
Yahya related to me from Malik from Abu’z Zinad from al-Araj from Abu Hurayra that the Messenger of Allah, may Allah bless him and grant him peace, mentioned the day of jumua and said, “There is a time in it when Allah gives to a muslim slave standing in prayer whatever he asks for,” and the Messenger of Allah, may Allah bless him and grant him peace, indicated with his hand how small it was.