Narrated Hafsa
When the Mu'adh-dhin pronounced the Adhan for Fajr prayer and the dawn became evident the Prophet ordered a two rak`at light prayer (Sunna) before the Iqama of the compulsory (congregational) prayer.
Narrated `Aisha
The Prophet (ﷺ) used to offer two light rak`at between the Adhan and the Iqama of the Fajr prayer.
Narrated `Abdullah bin `Umar
Allah's Messenger (ﷺ) said, "Bilal pronounces the Adhan at night, so keep on eating and drinking (Suhur) till Ibn Um Maktum pronounces the Adhan."