Are there any persons that Allah will not forgive?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Sins are of two kinds according to their forgiveness.

Firstly, the sins from which the person has repented.  These are of two kinds:

1)      Any sin apart from killing a Muslim without right.  These sins are forgiven if the repentance is sincere.

2)      Killing the Muslim without right. The majority of the scholars are of the opinion that even this major sin is also forgiven; the evidence is the saying of Allaah (which means): {And those who do not invoke with Allaah another deity or kill the soul which Allaah has forbidden [to be killed], except by right, and do not commit unlawful sexual intercourse. And whoever should do that will meet a penalty. Multiplied for him is the punishment on the Day of Resurrection, and he will abide therein humiliated. Except for those who repent, believe and do righteous work. For them Allaah will replace their evil deeds with good. And ever is Allaah Forgiving and Merciful…}[Quran 25: 68-70]; and the Hadeeth reported by al-Bukhari and Muslim about the man who killed 100 persons and repented and Allaah forgave him. 

However, Ibn 'Abbaas believes that the repentance of such a person is not accepted and his evidence is the saying of Allaah (which means): {And whoever kills a believer intentionally, his recompense is Hell to abide therein, and the Wrath and the Curse of Allaah are upon him, and a great punishment is prepared for him.}[Quran 4: 93]; and the Hadeeth narrated by Mu'aawiyyah that the Prophet, said: “Every sin is forgiven except a person who deliberately kills a Muslim or a person who dies as a non-Muslim (disbeliever).”[Abu Daawood]

The majority of the scholars believe that this ruling is limited to the person who believes that his act (killing a Muslim) is lawful.

Secondly, the sins from which the person did not repent.  These are of three kinds:

1)      A sin which Allaah does not forgive according to the consensus of the scholars.  This is polytheism.  Allaah Says (what means): {Verily, Allaah forgives not that partners should be set up with him in worship, …}[Quran 4: 48].

2)      A sin which Allaah forgives if He wishes and which are lesser than Shirk (polytheism) as Allah Says (what means): {…but He forgives except that (anything else) to whom He pleases, …}[Quran 4: 48].

3)      A sin about which the scholars differed in opinion whether such a sin is forgiven if Allaah so wishes or that it is a sin that Allaah does not forgive, like killing a Muslim without right.  The majority of the scholars believe that such a sin is under the Will of Allaah.  If He wishes, He forgives it and if He wishes He does not forgive it.   But as mentioned earlier, Ibn 'Abbaas,  believes that such a sin cannot be forgiven even if one had repented from it as already discussed.

Allaah Knows best.