Is it true that a Muslim will not enter Paradise until he pledges allegiance to an Imam or a ruler, as one of the Imams claims, citing hadiths and Quranic verses as evidence?

One must be wary of those who misinterpret texts such as "Whoever dies without an oath of allegiance (bay'ah) on his neck, dies the death of Jahiliyyah (pre-Islamic ignorance)" and apply them to factions of their own invention. Imam Ahmad explained the meaning of "Imam" in the hadith (definition) as "The Imam whom the Muslims gather upon. All of them say: 'This is the Imam.'"