What is the meaning of "a fire that emerges from Yemen will drive people to their place of gathering (mahshar)" in the hadiths about the major signs of the Hour, and does it mean gathering the living before their death to the land of gathering, or gathering them to the place of their death, and how is that possible when the earth will be changed on the Day of Resurrection?

The aforementioned Hadith is authentic, and its origin is in Sahih Muslim. It describes ten signs that precede the Hour, among them a fire that emerges from Yemen and drives people to their place of gathering. "Hashr" (gathering) linguistically means collection and driving. Religiously, it is divided into four types: First, the gathering of Banu Nadir from Medina to Ash-Sham. Second, the gathering of people by fire before the Trumpet blast of annihilation (which is the subject of the question). Third, the gathering of creation on the Day of Judgment. Fourth, the gathering of the pious to Paradise.

The gathering fire mentioned in the Hadith emerges from Yemen (the bottom of Aden). It has also been said that it emerges from the East. A reconciliation between the two is that its emergence begins from Aden and its spread extends to the East. This gathering occurs before the Hour, not after it, because it is mentioned among the minor signs of the Hour, and it describes situations of eating, drinking, sleeping, and traveling that can only exist in this world. This differs from the description of the gathering on the Day of Judgment, where people are gathered barefoot and naked. Furthermore, the Hadith indicates Ash-Sham as the place of gathering, which suggests that it occurs before the Day of Judgment.

In summary, the gathering fire drives people to the land of Ash-Sham before the Hour, where their souls will be taken.