Musnad Ahmad 33:1063

'Abd al-Razzaq narrated to us, Sufyan informed us, from al-A'mash, from Abu Sufyan, from Jabir, from al-Sulayk, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you comes to the Friday [prayer] while the Imam is delivering the sermon, let him pray two light rak'ahs."