Is the Sunnah of Fajr prayer performed after congregational Subh prayer?

If the Fajr prayer has been established, it is obligatory for the person entering with the Imam to join the congregational prayer. Then, he may perform the Sunnah of Fajr immediately afterward, and this is the most valid opinion based on what has been reported from Qays ibn Fahd. It is also permissible to delay performing the Sunnah until the time of Duha to avoid disagreement.