Musnad Abu Ya'la al-Mawsili 153:21

Abu Khaythama narrated to us, Ibn 'Uyaynah narrated to us, 'Amr narrated to us, from al-Zuhri, from Salim, from his father: That the Prophet, peace and blessings of Allah be upon him, used to pray two rak'ahs after the Friday prayer.