The Prophet said:
“The Jews split into 71 groups; one will enter Paradise and 70 will enter Hell. The Christians split into 72 groups; 71 will enter Hell and one will enter Paradise. By Him in Whose Power is the life of Muhammad, without doubt, my Ummah will be divided into 73 groups. Only one will enter Paradise and 72 will enter Hell.” (Ibn Majah, Kitab al-Fitan)
Also in Qur’an we find:
“Surely those who believe, and those who are Jews, and the Christians, and the Sabians, whoever believes in Allah and the Last day and does good, they shall have their reward from their Lord, and there is no fear for them, nor shall they grieve.” (Qur’an 2:62 and (almost identical in) 5:69)
This seems to indicate that salvation is dependent upon three conditions only: Belief in God, Belief in the Day of Judgement, and righteous or good deeds.
“Then shall anyone who has done an atom’s weight of good, see it! And anyone who has done an atom’s weight of evil, shall see it.” (Qur’an 99:7-8)
This suggests “anyone” or everyone will be rewarded for their good and bad actions. But will they go to Heaven or Hell? Allahu Alim.
Mr. Lamaan Ball, editor of “Ask About Islam”:
“When we refer to “Islam” there are at least two specific distinct meanings implied. Firstly there is the essential Islam as the religion of all the prophets from Adam, Noah, Abraham, Moses, Jesus and until Muhammad. Secondly there is the meaning specific to the revelation given to Muhammad and all the religious instructions contained therein. We might call this the completed Islam. Essential Islam encompasses the broad principles of pure monotheism free from shirk(associating partners with God), and our moral accountability before God. The completed Islam is the full set of guidance provided through the Qur’an and the sunnah of Muhammad which abrogates the earlier rules given through previous prophets.
Both 5:69 and 3:85 refer to the essential Islam and not the completed Islam we often mean in our conversations. Once this point is understood, the apparent problem disappears.
Second, the mere historical existence of Muhammad (pbuh) does not mean that the completed Islam has reached everyone. Once the completed Islam reaches any group of people, – by which I mean that the message is adequately delivered – then they can no longer claim to be doing good if they are knowingly rejecting God’s guidance in the Qur’an. Before that situation is reached, for any individual, it is quite possible that they are Muslims in the sense of following essential Islam. Just as the earliest followers of earlier prophets were.”
Allah knows best.