Musannaf Ibn Abi Shayba 3:6377

Al-Fadl ibn Dukayn narrated to us, from Abu al-Anbas, from Zadhan, from Ibn Umar, from Umar, who said: "The 'adbar al-nujum' (the retreating of the stars) are two rak'ahs before the dawn. And the 'adbar al-sujud' (the end of the prostrations) are two rak'ahs after the Maghrib."