Muslims believe that God alone decides who enters Paradise or Hell, and that He judges with perfect justice and mercy. No Muslim has the right to say that a particular person is in Hell.
The fuller answer
The Quran says that whoever seeks a religion other than Islam, it will not be accepted from them, and it also says that God does not punish any people until a messenger has come to them with a clear message. Scholars explain that those who never received the message of Islam clearly, or received it in a distorted form, are tested on the Day of Judgment and judged justly. The Quran also mentions groups of Jews, Christians and Sabians who believe in God and the last day and do good, and states they have their reward.
The Prophet ﷺ taught that God's mercy outweighs His anger. So Muslims hope for mercy for everyone, invite people to Islam with kindness, and leave the final judgment to God. Muslims do believe that knowing the truth and rejecting it is a serious matter.
Whoever is guided is only guided for [the benefit of] his soul. And whoever errs only errs against it. And no bearer of burdens will bear the burden of another. And never would We punish until We sent a messenger.
Indeed, those who believed and those who were Jews or Christians or Sabeans [before Prophet Muhammad] - those [among them] who believed in Allah and the Last Day and did righteousness - will have their reward with their Lord, and no fear will there be concerning them, nor will they grieve.
And decree for us in this world [that which is] good and [also] in the Hereafter; indeed, we have turned back to You." [Allah] said, "My punishment - I afflict with it whom I will, but My mercy encompasses all things." So I will decree it [especially] for those who fear Me and give zakah and those who believe in Our verses -
This answer follows the mainstream Sunni understanding and is general learning, not a fatwa. Where Muslims differ, the answer says so. Have a question of your own? Write to us.