It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to offer two rak'ahs between the call to Fajr prayer and the (Fajr) prayer itself.
Hadith Referenceمسند احمد / مسند النساء / 24968
Hadith Gradingحکم دارالسلام:حديث صحيح وإسناده كسابقه، خ: 619، م: 724