Musnad Ahmad 26:453

Yahya ibn Adam narrated to us, Sufyan narrated to us, from al-A’mash, from Ibrahim, from ‘Abd al-Rahman ibn Yazid, from Ibn Mas’ud, who said: "I prayed two rak'ahs with the Messenger of Allah, may Allah bless him and grant him peace. And I prayed two rak'ahs with Abu Bakr, may Allah be pleased with him, and two rak'ahs with ‘Umar, may Allah be pleased with him."