He proceeded from `Arafah shortly before sunset

A: The basic ruling is that pilgrims must remain in `Arafah on the ninth day of Dhul-Hijjah and not to leave until they ascertain that the sun has already set. It is not permissible for them to leave before that time. The important deciding factor is the setting of the sun. A pilgrim who leaves after ascertaining that the sun has set has fulfilled the obligation and there is nothing on them; but if they leave before sunset without having ascertained the time and do not return and remain there until sunset, or do not return even for a brief moment during the night, they must offer Dam (sacrificial animal offered as an atonement), which is to slaughter a sheep to compensate for neglecting an obligatory act of Hajj.