His statement, “leaves before sunset,” means that he leaves Mina before the sun sets, so that it may truly be said that he hastened his departure in two days. If he delays leaving until after sunset, he has not hastened his departure in two days, because the two days have passed.
His statement, “otherwise, he must stay overnight and perform the stoning the following day,” means that if he does not leave before sunset, he must stay overnight on the night of the thirteenth and stone the following day, after the sun has passed its zenith, just as on the two preceding days.
The evidence is that Allah says, “in two days” [al-Baqarah 2:203]. The word “in” denotes containment, and the container must necessarily be broader than what it contains. Accordingly, departure must take place within those two days.
It has been narrated from Umar—may Allah be pleased with him—that whoever is overtaken by evening must remain. (1)
Issue: Suppose a group has dismantled their tents, loaded their belongings, and set out, but their progress is held up by the large number of vehicles, so that the sun sets upon them before they have left Mina. They may continue their departure, because they were delayed through no choice of their own.
His statement, “When he intends to leave Mecca, he must not depart until he has performed the Farewell Tawaf”: the words, “he must not depart,” indicate prohibition, based on the hadith of Ibn Abbas—may Allah be pleased with him and his father—