Sahih Muslim Book 4, Hadith Number 1919.

Chapter : What is to be recited in the Jumu’a prayer ?.

‘Abdullah b. ‘Umar, while describing the Nafl prayer of the Messenger of Allah (may peace be upon him), said: He did not observe (Nafl) prayer after Jumu’a till he went back and observed two rak’ahs in his house. Yahya said: I guess that I uttered these words (before Imam Malik) that he of course observed (them).