Thank you for answering my last question about abiding in Hell by the people who commit sins other than Shirk. But I have few more questions on this topic. I hope you would clarify them.
Ibn Katheer and Al-Qurtubi said that 'Eternally' does not necessarily mean staying permanently in Hell. What is the evidence for this? Can you please cite any other verse of the Qur'aan or any classical Arabic texts to prove that?
On verse 25:68, you wrote that 'This' here refers to all the evil that was mentioned before including polytheism. Can you please explain why 'This' refers only to polytheism even though the preceding texts mention three sins together?
I also came across many Hadeeth which indicates permanent punishment in Hell for those who commit sins other than Shirk. Can you please explain them? The following are the Hadeeth.
Bukhaari, Muslim, may Allaah have mercy upon them, and others have narrated from Abu Hurayrah, may Allaah be pleased with him, that the Messenger of Allaah, sallallaahu alayhi wa sallam, said: "Whoever kills himself with a sharp instrument, then this sharp instrument will be in his hand and he will be stabbing himself in the stomach in the Fire of Hell, dwelling in it forever, and whoever kills himself with a poison, then his poison will remain in his hand forcing it into him in the Fire of Hell, dwelling in it forever, and whoever throws himself from a mountain and kills himself, so he will keep throwing himself down in the Fire of Hell, dwelling in it forever." Muslim has narrated in his book‚ from the Messenger of Allaah that he said: "Two types of the people of the Fire, I have not seen them: people having whips like the tails of the cow, they strike the people with them; and women wearing clothes [that show them] naked, seductive and seducing, their heads pointed like the humps of camels—they will not enter the Garden and will not get its fragrance, while its fragrance is felt for such a distance."
"Any ruler whom Allaah had given power over His subordinates and yet does rules unjustly, he will not smell even the fragrance of Paradise." [Bukhaari and others], and many more Hadeeth. Could you please enlighten us on this issue without bias?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Ibn Al-Qayyim stated that mentioning the abode and eternity does not necessarily mean that there is no end to it, but it means staying for a very long time, like saying an eternal bond. Everything has an eternity for itself, and this eternity could be for the length of the life of this world, as Allaah says (interpretation of meaning): {But never will they wish for it, ever, because of what their hands have put forth.}[2:95]. Ibn Al-Qayyim further said: 'It is known that they desire this in Hell as the saying of Allaah (interpretation of meaning): {And they will call, "O Maalik (Addressing the keeper of Hell) let your Lord put an end to us!"}[43:77]. You should know that there are firm principles in this field beyond which one is not allowed to go. If anything appears to be different from these firm principles, one has to balance them against these, and this is a very important matter. Among these firm principles is that the fate of a non-Muslim is Hell-fire where he will abide forever and ever and will never come out of it in any case. On the contrary, a Muslim will not abide forever and ever in Hell-fire even if he committed major great sins. The evidence for these principles is the saying of Allaah (interpretation of meaning): {Verily, Allaah forgives not that partners should be set up with him in worship, but He forgives except that (anything else) to whom He pleases.}[4:48]. The other evidence is what Al-Bukhari and Muslim reported that the Prophet said: "Jibreel (Gabriel) came to me and gave me glad tidings that whoever dies while not associating any partner with Allaah, will enter Paradise." So if you know this, it becomes clear to you that there is no problem in the texts that you have mentioned which apparently differ from what we have stated. The scholars have answers to this; we will summarize them in the following:

Some scholars are of the view that this applies to whomever thinks that those actions –mentioned in the question- are lawful. Some other scholars are of the view that these texts are mentioned to warn and condemn these actions. However, other scholars think that this is the punishment for them if Allaah wants to punish them, but He may forgive them if He so wishes, and there are other opinions. Anyway, Ahlus-Sunnah agree that the people who have committed major great sins will not abide in Hell-fire forever if they die believing in the Oneness of Allaah. However, the Mu'tazillah and Khawaarij deviate sects are of the view that the people who commit major great sins will be in the Hell-fire forever.

Allaah knows best.