[Sitting in one’s prayer place after Fajr]

Answer (and Allah grants success): There is nothing far-fetched in that. In the hadith: “Ḥajj is ʿArafah, and ʿUmrah is circumambulation of the House.” The exertion of remaining after Fajr resembles the exertion of standing at ʿArafah; indeed, the effort and burden on the soul of sitting after Fajr until sunrise may be greater for a person than ṭawāf and saʿy.
Thus the meaning would be: the reward for sitting in one’s place of prayer equals and matches the standing at ʿArafah and staying there, or equals ṭawāf and saʿy, or equals both.
This is the soundest way to understand it. It should not be taken to mean that the virtue of sitting equals the reward of an entire ḥajj with all its preliminaries—long travel, large expenditures, loading and unloading, fatigue, thirst, fear, hunger, leaving family, children, and homeland, exposure to heat and cold, and the like—and all that accompanies it. And in the report: “The reward is commensurate with the hardship.”
It should also be understood as referring to voluntary ḥajj, not the obligatory one, for in the report: “Those who draw nearest to Allah have not drawn near by anything like performing what He has made obligatory upon them,” or as he said.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1