Praise be to Allah, and peace and blessings be upon the Messenger of Allah.
The methodology of Ahl al-Sunnah wa al-Jama'ah in understanding the revealed texts is to reconcile them and refer ambiguous texts back to clear and decisive ones. Therefore, one text should not be taken in isolation from the rest of the evidence.
Killing oneself is one of the major sins, but it does not by itself take a Muslim outside Islam, unless it is accompanied by another act that nullifies faith. This is indicated by the saying of Allah:
﴿إِنَّ اللَّهَ لَا يَغْفِرُ أَن يُشْرَكَ بِهِ وَيَغْفِرُ مَا دُونَ ذَٰلِكَ لِمَن يَشَاءُ﴾ [النساء: 48]
“Indeed, Allah does not forgive associating partners with Him, but He forgives anything less than that for whom He wills.” [An-Nisa: 48]
Thus, the person who commits suicide is subject to the will of Allah: if He wills, He may forgive him; and if He wills, He may punish him according to his sin. Then his final destination will be Paradise as long as he died upon monotheism.
As for the hadiths that mention remaining in Hell or being forbidden from Paradise, they are not evidence that he will remain there eternally in the same way as the disbelievers. The word “remaining” may refer to a long period of stay, and it may be temporary, ending when the punishment ends. Likewise, being forbidden from Paradise may refer to a temporary prohibition, meaning that he does not enter it with those who enter first or at the outset.
One of the proofs that a person who commits suicide is not thereby a disbeliever is that the Prophet ﷺ did not expel a person who killed himself from the Muslim community. Rather, in some cases he refrained from leading the funeral prayer over him as a deterrent to people and to emphasize the gravity and sanctity of this act, while the Companions prayed over him.
It is also reported in Sahih Muslim, in the story of a man who killed himself, that he was forgiven because of his migration. This indicates that killing oneself does not necessarily entail disbelief.
Therefore, a person who commits suicide does not remain in Hell eternally merely because he committed suicide. Rather, he is a sinful Muslim who remains subject to the will of Allah. Allah may punish him and then bring him out of Hell, or He may pardon him through His mercy.
It is essential to exercise extreme caution regarding this grave sin, for the warning concerning it is severe. A Muslim must not surrender to despair or lose hope in the mercy of Allah.
And Allah knows best.