Musannaf Ibn Abi Shayba 3:6370

Abu Bakr narrated to us, he said: Ibn Mahdi narrated to us, from Sufyan, from Alwan ibn Abi Malik, from al-Sha'bi, who said: The "adbar al-sujud" (the ends of the prostrations) are two rak'ahs after the Maghrib prayer. And the "adbar al-nujum" (the ends of the stars) are two rak'ahs before the Fajr prayer.