Musannaf Ibn Abi Shayba 3:2997

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from his father, from Suhayl, from his father, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever among you is praying after the Jumu'ah, let him pray four."