Imam Bukhari narrates: Abu al-Yaman narrated to us, he said: Shu'aib informed us from al-Zuhri, he said: Urwah bin al-Zubair informed me that A'ishah, may Allāh be pleased with her, said that

when the mu'adhdhin fell silent after the first Adhan of Fajr (this refers to the Adhan before the Iqamah), the Prophet ﷺ would stand up and pray two light rak'ahs before the Fajr prayer, after the appearance of dawn, then he would lie down on his right side, until the mu'adhdhin came to him for the Iqamah.