Is departing from Mount Arafat before the Imam (leader of the Hajj) obligatory, and what is the penalty for leaving before him?
Chapter on Ransom (Fidyah) and Penalty for Hunting
Al-Mughni
Book of Hajj
Primary text
The apparent meaning is that departing before the Imam necessitates a sacrifice (Dam), even if it is after sunset. However, the correct view is that following the Imam in departure is not an obligation in all rites of Hajj, and therefore, departing with the Imam is not obligatory here. The companions' departure with the Prophet, peace be upon him, was habitual, not legally binding.
Supporting text
A narration from Ahmad indicates that departing before the Imam results in a penalty, and he strongly advised against leaving before the Imam. 'Ata also mandated a sheep if one departs before the Imam, though he differentiated between leaving 'Arafat and leaving Muzdalifah.