All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The narration that the questioner is referring to is reported by At-Tirmithi and narrated by Anas Ibn Maalik that the Prophet said: ''Whoever prays Fajr in congregation and sits mentioning Allaah until sunrise, then prays two Raka'h, he will get a complete reward of Hajj and 'Umrah, (he repeated 'complete reward' thrice)." And this is an authentic narration.
At-Tabaraani reported the same narration with a different wording, and narrated by Ibn 'Umar . The narration reads: ''The Prophet when he prays Fajr, used to remain sitting until he is able to pray again (i.e. after sunrise) and the Prophet said: ''Whoever prays Fajr and then remains in his position until he is able to pray again, it is as if he had performed an accepted Hajj and 'Umrah.''
So this is a great reward for whoever does so.Allaah knows best.