Is it permissible for a Muslim who worships Allah solely out of fear of Hellfire and wishes to become dust after escaping it, to ask for that, knowing that these beliefs are not a result of obsessive thoughts?

The worship of Allah is based on the fear of His punishment and the hope for His mercy, as the prophets did. There are two types of beliefs: cognitive, which are based on evidence, and non-cognitive, which are psychological in nature and not founded on knowledge. These psychological ideas may be from the whispers of Satan to prevent one from enjoying bliss. A Muslim must believe in the clear and decisive verses (muhkam), seek guidance from Allah, and hold fast to the Quran and Sunnah. Frequent remembrance of Allah and recitation of the Quran protect a Muslim from the whispers of Satan.