Musnad Ahmad 27:1031

'Affan narrated to us, Wuhayb narrated to us, 'Ubayd Allah ibn 'Umar narrated to us, from Nafi', from Ibn 'Umar (may Allah be pleased with them both): "That the Messenger of Allah (peace and blessings of Allah be upon him) used to pray two rak'ahs after the Jumu'ah (Friday prayer)."