Hazrat Ibn Sirin says that if a person enters the mosque during the congregation of Fajr, he should join the congregation and not offer the two Sunnah. Because the obligatory prayer that he would miss is of a higher status than the Sunnah.

Ibn Aun reports that I asked Ibrahim about this matter, and he replied that the missed obligatory prayers are to be made up, whereas missed voluntary prayers are not to be made up.

Hazrat Ibn Sirin says that the prayer missed with the Imam is better than these two rak‘ahs.

Hazrat Hammad says that do not enter the mosque without performing the two Sunnah of Fajr, even if you have to perform them on a heap of garbage.

Hazrat Ubaid bin Hasan narrates that I saw Hazrat Ibn Ma'qil performing the Sunnah of Fajr at the door of his house.

Hazrat Yahya bin Abi Kathir says that if a person comes to the mosque during the Fajr prayer, he should not offer the Sunnah of Fajr before the Fajr prayer, rather he should perform them at the time of Duha.

Hazrat Saeed bin Jubair says that if there is a place other than the mosque, then offer these Sunnahs there; do not offer them in the mosque.

Hazrat Ata says that if a person fears missing one rak‘ah of the obligatory prayers, then he should leave these sunnahs and join the congregation.

Hazrat Abu Ja'far narrates that once the Prophet (peace be upon him and his family) came to the mosque for the Fajr prayer, and Hazrat Bilal began the Iqamah. Hazrat Ibn Buhaina stood up to offer the two Sunnah of Fajr, so the Prophet (peace be upon him and his family) placed his hand on his shoulder and said, "O Ibn Qushab! Will you offer four rak'ahs of Fajr?"

Hazrat Ibn Buhaina narrates that once the iqamah for the morning prayer was given, and a man stood up to offer two sunnah rak'ahs. When the Prophet (peace and blessings be upon him) had completed the prayer, people gathered around him. He said to the person who had offered the two sunnah rak'ahs, "Do you offer four rak'ahs for Fajr?"