Musnad Ahmad 482:121

Abu Abd al-Rahman narrated to us, Ibn Lahi'ah narrated to us, from Mushrih ibn Ha'an, from Uqbah ibn Amir, who said: I said, "O Messenger of Allah, has Surah al-Hajj been favored over the [rest of the] Qur'an by having two prostrations placed in it?" He said, "Yes, and whoever does not perform them, let him not recite them."