Salvation in Islam

"Salvation" in Islam refers to the eventual entrance to heaven. The word does not cover the possible entry to hellfire, or the different levels of hellfire and heaven. The Quran teaches that the only thing guaranteeing no salvation is a disbelief in the “One God”; associating others with God,

Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth; to set up partners with Allah is to devise a sin Most heinous indeed.^{[Qur'an 4:48]}

The above verse is referring to the forgiveness in the hereafter. Those who die believing not in the “One God” do not receive salvation. Those who die believing in the “One God”, but disbelieving in his message (Islam), are left to his will; God might forgive them, or might not. Those who die believing in the “One God” and his message “Islam” receive salvation. Narrated Anas that Mohammad said,

Whoever said "None has the right to be worshipped but Allah" and has in his heart good (faith) equal to the weight of a barley grain will be taken out of Hell. And whoever said, "None has the right to be worshipped but Allah" and has in his heart good (faith) equal to the weight of a wheat grain will be taken out of Hell. And whoever said, "None has the right to be worshipped but Allah" and has in his heart good (faith) equal to the weight of an atom will be taken out of Hell.

—Prophet Mohammad Sahih al-Bukhari, 1:2:42

A person who becomes a Muslim must testify that "none has the right to be worshiped but Allah" indicating the belief in the One God, and "Mohammad is Allah's Apostle" indicating the belief in God's message.
Islam teaches that if one wishes to enter heaven, and avoid hellfire completely, one must believe in the "One God", and obey him following his message. There is no other way. The Quran states,

If anyone desires a religion other than Islam (submission to Allah), never will it be accepted of him; and in the Hereafter He will be in the ranks of those who have lost (All spiritual good).^{[Qur'an 3:85]}

Belief in the “One God”

See also: Tawhid, Jannah, and Repentance in Islam

Belief in the “One God”, also known as the Tawheed (التَوْحيدْ) in Arabic, is broken into two parts (or principals):

1. Tawheedo Al Ruboobeeya ( تَوْحيدُ الرُبوبِيَّة): Believing in the attributes of God and attributing them to no other but God. Such attributes include Creation, having no beginning, and having no end. These attributes are what make a God. Islam also teaches 99 names for God, and each of these names defines one attribute. One breaks this principle, for example, by believing in an Idol as an intercessor to God. The idol, in this case, is thought of having powers that only God should have, thereby breaking this part of Tawheed. No intercession is required to communicate with, or worship, God.
2. Tawheedo Al Ilooheeya (تَوْحيدُ الإِلوهيَّة): Directing worship, prayer, or deed to God, and God only. For example, Worshiping a planet, or God along with a creation, or multiple Gods, breaks this principle, and consequently breaks the Tawheed.

Tawheedo Al Ruboobeeya is seen to “imply” Tawheedo Al Ilooheeya, because it is seen that that who has the attributes of a God deserves to be worshiped.
Some Muslim scholars break the Tawheed into further parts by breaking Tawheedo Al Ruboobeeya into multiple parts putting emphases on some of the attributes of God that they see being vastly ignored, or forgotten, in their respective times. Many scholars, for example, state a third principle, Tawheedo Al Asma'a (تَوْحيدُ الأَسْماءْ) which explicitly states the belief in the names of God. Other scholars state another principal, Tawheedo Al Hukmee (تَوْحيدُ الحُكْم), which explicitly states the belief in the Governance Attribute of God, emphasizing this attribute which is a part of Tawheed seen to be vastly broken by modern governments of Muslim nations which do not follow the Islamic law.


 
The Test
To avoid hell, one must also avoid sin; belief is not enough; Islam acknowledges the inclination of man towards sin^{[Qur'an 3:85][Qur'an 12:51-53]}. A Muslim must think of his sin, seek God's forgiveness and repent. However, this repentance must be sincere, and God's mercy must not be taken as a license to sin further. Islam teaches that God is Merciful, but it also teaches that he is wise. The Quran states:

Allah accept the repentance of those who do evil in ignorance and repent soon afterwards; to them will Allah turn in mercy: For Allah is full of knowledge and wisdom.<17> Of no effect is the repentance of those who continue to do evil, until death faces one of them, and he says, "Now have I repented indeed;" nor of those who die rejecting Faith: for them have We prepared a punishment most grievous.<18> ^{[Qur'an 4:17]}

Islam teaches that every person, including man, woman and prophet, is responsible for his/her own sins. A Muslim must be aware of his sin, and repent. The Quran states,

If ye reject (Allah), Truly Allah hath no need of you; but He liketh not ingratitude from His servants: if ye are grateful, He is pleased with you. No bearer of burdens can bear the burden of another. In the end, to your Lord is your Return, when He will tell you the truth of all that ye did (in this life). for He knoweth well all that is in (men's) hearts. ^{[Qur'an 39:7]}

Al-Agharr al-Muzani, a companion of Mohammad, reported that Ibn 'Umar stated to him that Mohammad said,

O people, seek repentance from Allah. Verily, I seek repentance from Him a hundred times a day.

—Prophet Mohammad Sahih Muslim, 35:6523

Sin in Islam is not a state, but an action (a bad deed); Islam teaches that a child who dies young, regardless of the belief of his parents, dies a Muslim; he enters heaven, and does not enter hell. Sahih al-Bukhari, 2:23:467
A Muslim must also think of heaven. The matter is not as simple as entering hellfire or entering heaven. Both hellfire and heaven have levels. A Muslim seeks to enter heaven and aims for the highest level. He does this by increasing his good deeds. In the Quran, whenever those who enter heaven are mentioned, and the virtue of belief is mentioned, it is coupled with the mention of good deeds. Some examples are,

But those who believe and work righteousness will be admitted to gardens beneath which rivers flow,- to dwell therein for aye with the leave of their Lord. Their greeting therein will be: "Peace!" ^{[Qur'an 14:23]}

But those who believe and do deeds of righteousness,- we shall soon admit them to gardens, with rivers flowing beneath,-to dwell therein for ever. Allah's promise is the truth, and whose word can be truer than Allah's? ^{[Qur'an 4:122]}

That He may reward those who believe and work deeds of righteousness: for such is Forgiveness and a Sustenance Most Generous." ^{[Qur'an 34:4]}

A Muslim does not believe that his good deeds merit him heaven, instead it is God's mercy on the people that lets them into heaven. The levels in heaven (and hell) are only a direct result of God's justice: those who do better, deserve better. Narrated Aisha, that Mohammad said,

"Do good deeds properly, sincerely and moderately, and receive good news because one's good deeds will not make him enter Paradise." They asked, "Even you, O Allah's Apostle?" He said, "Even I, unless and until Allah bestows His pardon and Mercy on me." Sahih al-Bukhari, 8:76:474

Those with belief will eventually enter heaven, but only after they are punished for their sins (those that God did not forgive). God forgives sins but it is not a guarantee. Therefore, a Muslim must keep a balance between fear of God, and hope in his mercy. One who does not have this balance is in danger of losing his belief; one who has absolute hope in God's mercy and no fear of his wrath will end up sinning, believing God will forgive him regardless, and one who has absolute fear of God's wrath and no hope in his mercy will also end up sinning, believing himself entering hellfire regardless.

Mandatory acts of worship

There are acts of worship that Islam teaches to be mandatory. Islam is built on five principles. Narrated Ibn 'Umar that Muhammad said,

Islam is based on (the following) five (principles):

1. To testify that none has the right to be worshipped but Allah and Muhammad is Allah's Apostle.
2. To offer the (compulsory congregational) prayers dutifully and perfectly.
3. To pay Zakat to poor and needy (i.e. obligatory charity of 2.5% annually of surplus wealth) .
4. To perform Hajj. (i.e. Pilgrimage to Mecca)
5. To observe fast during the month of Ramadhan. Sahih al-Bukhari, 1:2:7

Not performing the mandatory acts of worship is a sin. See also Shirk. A person who becomes a Muslim must testify that "none has the right to be worshiped but Allah" indicating the belief in the One God, and "Mohammad is Allah's Apostle" indicating the belief in God's message and thereby obeying his commands. The Quran states.

... This day have I perfected your religion for you, completed My favour upon you, and have chosen for you Islam as your religion. ... ^{[Qur'an 5:3]}

Redemption

Redemption is a religious concept referring to forgiveness or absolution for past sins or errors and protection from damnation and disgrace, eternal or temporary, generally through sacrifice. Redemption is common in many world religions, including Indic religions and all Abrahamic Religions, especially in Christianity and Islam (المغفرة).
In Judaism, (Hebrew ge'ulah), redemption refers to God redeeming the people of Israel from their various exiles.^[69] This includes the final redemption from the present exile.
In Christianity, redemption is synonymous with salvation. The Christian religion, though not the exclusive possessor of the idea of redemption, has given to it a special definiteness and a dominant position. Taken in its widest sense, as deliverance from dangers and ills in general, most religions teach some form of it. It assumes an important position, however, only when the ills in question form part of a great system against which human power is helpless.^[70]
In some forms of Buddhism, redemption is inherent in the discipline of giving up attachments to desires. Theravada Buddhism teaches that in this quest one can rely on no one and on nothing but oneself: neither gods nor priests, neither church nor sacraments, nor faith nor works are of any avail.^[71] Other disciplines are not so desolate, and "each Buddha and Bodhisattwa is a redeemer", assisting the Buddhist in seeking to achieve the redemptive state.^[72] The assistance rendered is a form of self-sacrifice on the part of the teachers, who would presumably be able to achieve total detachment from worldly concerns, but have instead chosen to remain engaged in the material world to the degree that this is necessary to assist others in achieving such detachment.^[72]