Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1916
Suhail reported on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) said: When you observe prayer after (the two obligatory raklabs) of Jumu'a, you should observe four rak'ahs (and 'Amr in his narration has made this addition that Ibn Idris said this on the authority of Suhail): And if you are in a hurry on account of something, you should observe two rak'ahs in the mosque and two when you return (to your house).