Salam. In fatwa 393448 you said: "it should be mentioned that the Islamic sects who will enter Hellfire because of deviating from the guidance of the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) will ultimately enter Paradise even if they have entered Hellfire beforehand".
Where does it say in the Sunna or any other book that they will be saved? Please, I need hard facts.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The creed of the Ahlus-Sunnah Wal-Jamaa‘ah regarding Muslim sinners who die while not committing Shirk (polytheism) is that they shall not abide eternally in Hellfire, regardless of the gravity of the sin they committed. This is evidenced by many Sharee‘ah texts which state that anyone who has in his heart faith equal to the weight of an atom will not abide in Hellfire eternally and will eventually come out of Hellfire if he enters it. It was narrated on the authority of Abu Sa‘eed Al-Khudri, may Allaah be pleased with him, that the Prophet said: “When the People of Paradise will have entered Paradise, and the People of the Hellfire will have entered the Hellfire, Allah will say (to the Angels): 'Take out (of Hellfire) whoever has got faith equal to the weight of a grain of mustard seed.' They will come out, and by that time, they will have burnt and become like coal, and then they will be thrown into the river of Hayaah (life), and they will spring up just as a seed grows on the bank of a rainwater stream.” [Al-Bukhaari and Muslim]

No matter how grave a sin may be, it does not entail abiding in Hellfire eternally, unless it is the sin of Shirk that takes a Muslim out of the fold of Islam. At-Tahaawi said: “The Muslim sinners who commit grave major sins will not abide in Hellfire perpetually if they die while adhering to Tawheed (Islamic monotheism).” [End of Quote]

Shaykh Al-Islaam Ibn Taymiyyah said: “The established principle of the Ahlus-Sunnah Wal-Jamaa‘ah regarding Muslim sinners (who die before repenting of their sins) is that they shall not abide eternally in Hellfire, contrary to the view of the Mu‘tazilah (Mu‘tazilites) and Khawaarij (Kharijites).” [End of Quote]

The groups affiliated to Islam who deviate from the straight path are considered among the Muslim sinners who hold onto Tawheed as long as their deviation does not lead them to Kufr (disbelief), which takes a doer out of the fold of Islam. Any adherent of such groups who dies while persisting in committing that Sharee‘ah violation after having been educated beyond the excuse of ignorance, the forgiveness of his sin is subject to the Will of Allah, The Exalted, just like other Muslim sinners of the same standing. Even if Allah, The Almighty, punishes them, they will not abide in Hellfire eternally.

We would like to warn the Muslim youth against the gravity of going to extremes in labeling and judging people, especially declaring Muslims to be disbelievers. The fact that some Muslims have committed Sharee‘ah violations does not permit labeling and judging them with what they do not deserve under the Sharee‘ah. Allah, The Exalted, commanded that we be just as He Says (what means): {…And when you testify, be just…} [Quran 6:152] Moreover, the Prophet said: “O people, beware of exaggeration in religious matters, for those who came before you were doomed because of exaggeration in religious matters.” [An-Nasaa’i and Ibn Maajah]

For more benefit that the believers who sinned will not abide in Hellfire eternally, please refer to Fatwa 341239.

Allah Knows best.