Musannaf Ibn Abi Shayba 3:3049

Abu Usama narrated to us, he said: Abd al-Malik ibn Abi Sulayman narrated to us, he said: Ata’ narrated to us, he said: I saw Ibn Umar pray Jumu'ah, then he moved aside from his place and prayed two rak'ahs in which there was lightness. Then he moved aside from that place and prayed four [rak'ahs] that were longer than those two.