Musannaf Ibn Abi Shayba 3:1910

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mansur, from Ibn Sirin, from Ibn Umar, from Umar, that he prostrated twice in [Surat] al-Hajj. Then he said: "Indeed, this Surah has been favored over the rest of the Surahs by two prostrations."