Musnad Ahmad 2:176

Waki’ narrated to us, Sufyan and ‘Abd al-Rahman narrated to us, from Sufyan, from Zubayd al-Yamami, from ‘Abd al-Rahman ibn Abi Layla, from ‘Umar, who said: The prayer of travel is two rak’ahs, the prayer of al-Adha is two rak’ahs, the prayer of al-Fitr is two rak’ahs, and the prayer of Jumu’ah is two rak’ahs, complete and not shortened, upon the tongue of Muhammad, may Allah bless him and grant him peace. Sufyan said: And Zubayd said once: I think it is from ‘Umar. ‘Abd al-Rahman said: Without any doubt. And Yazid—meaning Ibn Harun—said: Ibn Abi Layla said: I heard ‘Umar.