What is the legal ruling on the action of an Imam who prolongs the Tarawih prayer to nearly three hours, distinguishing between verses of torment with "Ameen" and verses of blessing with "Ameen"? And did the Messenger of Allah, peace and blessings be upon him, do this when praying alone or as an Imam?

The issue of a worshiper supplicating when passing by a verse of mercy or punishment has a precedent in the actions of the Prophet, peace and blessings be upon him. He used to pause and ask (for mercy) when encountering a verse of mercy, and seek refuge (from punishment) when encountering a verse of punishment. Scholars have differed on the ruling concerning this: The Shafi'is deemed it recommendable for every worshiper. The Hanafis, however, deemed it disliked for both the imam and the congregant. The Malikis disliked it only in obligatory prayers. As for the Hanbalis, there are two narrations: one for its recommendability and another for its disliking in obligatory prayers. If the imam supplicates during recitation, it appears that the congregant should not say "Amen" to his supplication.