The Mercy of Almighty Allah is so great that one should never despair whether or not his Lord will forgive him.
Apart from the act of Shirk (associating partners with Allah), all sins are forgiven when the sinner turns to repent sincerely for his actions.
It is stated in the Holy Qur’an:
“Proclaim, O dear Muhammad: ‘O my slaves, who have wronged themselves, do not lose hope in Allah’s mercy; indeed Allah forgives all sins; indeed only He is the Oft Forgiving, the Most Merciful.’”
[Holy Qur'an 39:53]
“…He said, “I give My punishment to whomever I will; and My mercy encompasses all things; so I shall soon destine favours for those who fear and pay the charity, and they believe in Our signs.”
[Holy Qur'an 7:156]
Hadith Sharif about His Mercy
Narrated by Hazrat Abu Huraira, Sayyidina Rasulallah said, “When Allah completed the creation, He wrote in His Book which is with Him on His Throne, “My Mercy overpowers My Anger.”
[Sahih Bukhari - Book 54, Hadith no. 416]
Hazrat Anas ibn Malik said, “I heard the Messenger of Allah say:
“Allah said, ‘O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you and I would not mind.’”
[Tirmidhi, Hadith no. 3540]
Allah’s Forgiveness Overpowers His Wrath
Sayyidina Rasulallah said:
“There was a man who had heartlessly murdered ninety-nine people. Then, he felt remorse.
He went to a learned man and told him about his past, explaining that he wished to repent, reform, and become a better person.
“I wonder if Allah will pardon me?” he asked.
For all his learning, the scholar was a man who had not been able to digest what he had learned.
“You will not be pardoned”, he said. “Then I may as well kill you too,” said the other. And kill him, he did.
He then found another worthy individual and told him that he had killed a hundred people.
“I wonder,” he said, “whether Allah will pardon me if I repent?”
Being a truly wise man, he replied, “Of course you will be pardoned; repent at once. I have just one piece of advice for you: avoid the company of wicked people and mix with good people, for bad company leads one into sin.”
The man expressed repentance and regret, weeping as he sincerely implored his Lord to pardon him. Then, turning his back on bad company, he set off to find a neighborhood where righteous people lived.
On the way, his appointed hour arrived, and he died. The Angels of Punishment and the Angels of Mercy both came to take away his soul.
The Angels of Punishment said that as a sinful person, he rightfully belonged to them, but the Angels of Mercy also claimed him, saying, “He repented and had resolved to become a good man. He was on his way to a place where righteous people live, but his appointed hour had come.”
A great debate ensued, and Hazrat Jibra’il was sent as an arbitrator to settle this affair.
After hearing both sides he gave this verdict: “Measure the ground. If the spot where he died is closer to the good people, then he belongs to the Angels of Mercy, but if it is nearer to the wicked people, he will be given to the Angels of Punishment.”
They measured the ground. Because the man had just set out, he was still closer to the wicked. But because he was sincere in his repentance, the Merciful Lord moved the spot where he lay and brought it just outside the city of the pious people.
That penitent servant was then handed over to the Angels of Mercy.”
[Sahih Bukhari - Volume 4, Book 56, Number 676]