Entering the mosque while people are praying Fajr, then starting the two rak'ahs of the sunnah, and then catching up with the congregation

Q: We notice that some people, when they enter the mosque for the Fajr prayer and the prayer has already been called for, pray the two rak'ahs of Fajr and then catch up with the imam. What is the ruling on that? And is it better to pray them immediately after Fajr, or to wait until the sun rises?

A: It is not permissible for one who enters the mosque and the prayer has already been called for to pray a rawatib or the greeting of the mosque. Rather, it is obligatory for him to enter with the imam in the current prayer. This is based on the saying of the Prophet (peace and blessings be upon him): , which Imam Muslim recorded in his Sahih. This hadith covers the Fajr prayer and other prayers.
Then he has a choice: if he wishes, he prays the rawatib after the prayer, and if he wishes, he delays them until after the sun has risen, and that is better. This is because it is authentically reported from the Prophet (peace and blessings be upon him) what indicates both of these options.
And success is from Allah.