Qâdîzâde Ahmad Affandi (d. 1197/1783) rahimahullah stated:
"Janna [Paradise] and Jahannam [Hell] and those who reside in them are eternal. Contradicting this fact causes kufr [disbelief]. May Allahu ta'ala protect us." (Sharh of Wasiyyat of Birgivî [In Turkish], Bedir Publishing, Istanbul, p. 124)
Ibn Hazm wrote:
"... They have agreed with consensus that Jahannam is haq [true], that it is an eternal place of punishment, and that it [Jahannam] and its inhabitants will continue forever and will never cease to exist." (Maratib al-Ijma', 268)
Imam al-Subkî rahimahullah states:
"The doctrine of the Muslims is that Paradise and Hellfire do not pass away. Abû Muhammad Ibn Hazm has reported Ijma [Consensus] on the question and the fact that whoever violates such Consensus is a disbeliever (kâfir) by Consensus. There is no doubt over this, for it is obligatorily known in the Religion and the evidence to that effect is abundant." (Al-Subkî, al-Durra al-Mudiyya fî al-Radd `alâ Ibn Taymiyya (3rd epistle, al-I`tibâr bi Baqâ' al-Jannati wa al-Nâr p. 60), quoted by Dr. J. F. Haddad).
Imam al-Ash`ari rahimahullah stated:
"The whole of Ahl al-Islam stated the following: 'There is no end to Janna and Jahannam. Both of them will continue to exist. In the same way, people of Janna will continue to be rewarded [given benefactions] and the people of Jahannam will continue to be punished. There is no end to this.' " (Maqalat al-Islamiyyin, 164)
Imam al-Kawthari rahimahullah stated that:
"The takfîr [declaration of apostasy] of those who deny the eternality of Janna and Jahannam or one of them [Janna or Jahannam] is based on the Ijma of Ahl al-Haq [people of truth]." (Maqalat, 377)
"That Janna and Jahannam are eternal is fixed by Qur'an al-Karîm, the Sunna and yaqini [definite] ijma." (Maqalat, 450)
Imam al-a'zam Abu Hanifa rahimahullah stated:
"One who says that Janna and Jahannam will cease to exist after people of Janna and people of Jahannam enter [Janna and Jahannam, respectively] becomes kâfir [apostate] because of denying eternal staying there [in Janna and Jahannam]." (al-Fiqh al-Absat)
Imam al-Tahawi rahimahullah wrote:
Janna and Jahannam have been created; they will not ever cease to exist.
Imam al-Tahawi also wrote:
People who commit great sins among the umma [community, believers] of Muhammad (sallallahu ta'ala alayhe wa sallam) will not abide in Hellfire forever, provided that they die as Ahl al-Tawhid [as monotheists, i.e. as Muslims]. This includes even the unrepentant that, nonetheless, died as believers knowing Allahu ta'ala. They are in His judgment and decree. If He wishes, He forgives and pardons them by His grace, as He mentioned in His book (4:48). Or if He wishes, He punishes them in Hellfire by His justice, and then removes them by His rahmat [mercy, grace], (or) through the intercession of His obedient servants. He then sends them to His Janna [Paradise].
(additional quotes to be added inshaAllahu ta'ala)