Sahih al-Bukhari Book 10, Hadith 22
"When the Mu'adh-dhin pronounced the Adhan, some of the companions of the Prophet (ﷺ) would
proceed to the pillars of the mosque (for the prayer) till the Prophet (ﷺ) arrived and in this way they used
to pray two rak`at before the Maghrib prayer. There used to be a little time between the Adhan and the
Iqama." Shu`ba said, "There used to be a very short interval between the two (Adhan and Iqama).
Allah's Messenger (ﷺ) said thrice, "There is a prayer between the two Adhans (Adhan and Iqama)," and added, "For the one who wants to pray."
Allah's Messenger (ﷺ) used to pray two light rak`at before the morning (compulsory) prayer after the day dawned and the Mu'adh-dhin had finished his Adhan. He then would lie on his right side till the Mu'adh-dhin came to pronounce the Iqama.