The quran tells us a number of times that those who disbelieved and took partners with Allah (SWT), they are خالدين فيها ابدا (They will abide forever). As for those who believed in Allah (SWT) and took no partners with Allah (SWT), with the mercy of Allah will eventually go Jannah.
Not all people of jahannam. Allah allows the Prophet sallallahu 'alayhi wa salaam to intercede for muslims who enter jahannam.
[FONT="]‘Awf bin Malik Al-Ashja’i said:[/FONT] [FONT="]“The Messenger of Allah (ﷺ) said: ‘Do you know what choice my Lord gave me on this night?’ We said: ‘Allah and His Messenger know best.’ He said: ‘He gave me the choice between admitting half of my nation to Paradise and intercession, and I chose intercession.’ We said: ‘O Messenger of Allah, pray that we will be among its people (the people for whom you will intercede).’ He said: ‘It is for every Muslim.’” (Sunan Ibn Majah)
[/FONT] [FONT="]It was narrated from ‘Imran bin Husain that the Prophet (ﷺ) said:[/FONT] [FONT="]“Some people will be brought forth from Hell by my intercession, who will be called Al-Jahannamiyyin (those who came out of Hell).” (Sunan Ibn Majah)
Ja'far bin Muhammad narrated from his father, from Jabir bin 'Abdullah who said:
"The Messenger of Allah (s.a.w)said: 'My intercession is for the people who comitted major sins in my Ummah.'" Muhammad bin 'Ali said: "Jabir said to me: 'O Muhammad! Whoever is not among the peole of major sins, then there is no need in the intercession for him.'" (Jami'at-Tirmidhi)
Except those destined for Jahannam (imprisoned by the Qur'an) :
(part of hadith, the actual hadith is longer) So they will come to me, and I will ask my Lord's permission to enter His House and then I will be permitted. When I see Him I will fall down in prostration before Him, and He will leave me (in prostration) as long as He will, and then He will say, 'O Muhammad, lift up your head and speak, for you will be listened to, and intercede, for your intercession will be accepted, and ask (for anything) for it will be granted:' Then I will raise my head and glorify my Lord with certain praises which He has taught me. Allah will put a limit for me (to intercede for a certain type of people) I will take them out and make them enter Paradise." (Qatada said: I heard Anas saying that), the Prophet (ﷺ) said, "I will go out and take them out of Hell (Fire) and let them enter Paradise, and then I will return and ask my Lord for permission to enter His House and I will be permitted.When I will see Him I will fall down in prostration before Him and He will leave me in prostration as long as He will let me (in that state), and then He will say, 'O Muhammad, raise your head and speak, for you will be listened to, and intercede, for your intercession will be accepted, and ask, your request will be granted.' " The Prophet (ﷺ) added, "So I will raise my head and glorify and praise Him as He has taught me. Then I will intercede and He will put a limit for me (to intercede for a certain type of people). I will take them out and let them enter Paradise." (Qatada added: I heard Anas saying that) the Prophet said, 'I will go out and take them out of Hell (Fire) and let them enter Paradise, and I will return for the third time and will ask my Lord for permission to enter His house, and I will be allowed to enter.
When I see Him, I will fall down in prostration before Him, and will remain in prostration as long as He will, and then He will say, 'Raise your head, O Muhammad, and speak, for you will be listened to, and intercede, for your intercession will be accepted, and ask, for your request will be granted.' So I will raise my head and praise Allah as He has taught me and then I will intercede and He will put a limit for me (to intercede for a certain type of people). I will take them out and let them enter Paradise." (Qatada said: I heard Anas saying that) the Prophet (ﷺ) said, "So I will go out and take them out of Hell (Fire) and let them enter Paradise, till none will remain in the Fire except those whom Quran will imprison (i.e., those who are destined for eternal life in the fire)." The narrator then recited the Verse:-- "It may be that your Lord will raise you to a Station of Praise and Glory.' (17.79) The narrator added: This is the Station of Praise and Glory which Allah has promised to your Prophet. (Sahih al Bukhari)
The quran tells us a number of times that those who disbelieved and took partners with Allah (SWT), they are خالدين فيها ابدا (They will abide forever). As for those who believed in Allah (SWT) and took no partners with Allah (SWT), with the mercy of Allah will eventually go Jannah.l