Imam Ahmad recorded that `Abdullah bin Mas`ud said, "The Messenger of Allah was asked which sin is the most serious" He said:
«أَنْ تَجْعَلَ للهِ نِدًّا وَهُوَ خَلَقَك»
(That you appoint a rival to Allah when He has created you.) He asked, "Then what" He said:
«أَنْ تَقْتُلَ وَلَدَكَ خَشْيَةَ أَنْ يَطْعَمَ مَعَك»
(That you kill your child for fear that he may eat with you.) He said, "Then what" He said:
«أَنْ تُزَانِي حَلِيلَةَ جَارِك»
(That you commit adultery with your neighbor's wife.) `Abdullah said, "Then Allah revealed, confirming that:
وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَـهَا ءَاخَرَ
(And those who invoke not any other god along with Allah....)" This was also recorded by An-Nasa'i, and by Al-Bukhari and Muslim. It was narrated that Sa`id bin Jubayr heard Ibn `Abbas saying that some of the people of Shirk killed a great deal and committed Zina a great deal, then they came to Muhammad ﷺ and said: "What you are saying and calling people to is good, if only you would tell us that there is a way to expiate for what we have done." Then the Ayah:
وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَـهَا ءَاخَرَ
(And those who invoke not any other god along with Allah...) was revealed, as was the Ayah,
قُلْ يعِبَادِىَ الَّذِينَ أَسْرَفُواْ عَلَى أَنفُسِهِمْ
(Say: "O My servants who have transgressed against themselves!") (39:53).
وَمَن يَفْعَلْ ذلِكَ يَلْقَ أَثَاماً
(and whoever does this shall receive Athama.) It was recorded that `Abdullah bin `Amr said: "Athama is a valley in Hell." `Ikrimah also said that Athama refers to valleys in Hell in which those who commit unlawful sexual acts will be punished. This was also narrated from Sa`id bin Jubayr and Mujahid. As-Suddi said that Athama referred to punishment, which is closer to the apparent meaning of the Ayah. This interpretation makes it interchangeable with what comes next, the Ayah:
يُضَـعَفْ لَهُ الْعَذَابُ يَوْمَ الْقِيـمَةِ
(The torment will be doubled for him on the Day of Resurrection,) i.e., repetitive and intensified.
وَيَخْلُدْ فِيهِ مُهَاناً
(and he will abide therein in disgrace;) scorned and humiliated.
إِلاَّ مَن تَابَ وَءَامَنَ وَعَمِلَ عَمَلاً صَـلِحاً
(Except those who repent and believe, and do righteous deeds;) means, those who do these evil deeds will be punished in the manner described,
إِلاَّ مَن تَابَ
(Except those who repent), that is; those who repent in this world to Allah from all of those deeds, for then Allah will accept their repentance. This is evidence that the repentance of the murderer is acceptable, and there is no contradiction between this and the Ayah in Surat An-Nisa':
وَمَن يَقْتُلْ مُؤْمِناً مُّتَعَمِّداً
(And whoever kills a believer intentionally) (4:93), because even though this was revealed in Al-Madinah, the meaning is general, and it could be interpreted to refer to one who does not repent, because this Ayah states that forgiveness is only for those who repent. Moreover Allah says:
إِنَّ اللَّهَ لاَ يَغْفِرُ أَن يُشْرَكَ بِهِ وَيَغْفِرُ مَا دُونَ ذَلِكَ لِمَن يَشَآءُ
(Verily, Allah forgives not that partners should be set up with Him, but He forgives except that to whom He wills) (4:48). And in the authentic Sunnah, it is reported from the Messenger of Allah ﷺ that the repentance of a murderer is acceptable, as was stated in the story of the person who killed one hundred men and then repented, and Allah accepted his repentance, and other Hadiths.
فَأُوْلَـئِكَ يُبَدِّلُ اللَّهُ سَيِّئَاتِهِمْ حَسَنَـتٍ وَكَانَ اللَّهُ غَفُوراً رَّحِيماً
(for those, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful.) Imam Ahmad recorded that Abu Dharr, may Allah be pleased with him, said, "The Messenger of Allah ﷺ said:
«إِنِّي لَأَعْرِفُ آخِرَ أَهْلِ النَّارِ خُرُوجًا مِنَ النَّارِ، وَآخِرَ أَهْلِ الْجَنَّةِ دُخُولًا إِلَى الْجَنَّةِ، يُؤْتَى بِرَجُلٍ فَيَقُولُ: نَحُّوا عَنْهُ كِبَارَ ذُنُوبِهِ وَسَلُوهُ عَنْ صِغَارِهَا، قَالَ: فَيُقَالُ لَهُ: عَمِلْتَ يَوْمَ كَذَا، كَذَا وَكَذَا، وَعَمِلْتَ يَوْمَ كَذَا، كَذَا وَكَذَا، فَيَقُولُ: نَعَمْ لَا يَسْتَطِيعُ أَنْ يُنْكِرَ مِنْ ذَلِكَ شَيْئًا، فَيُقَالُ: فَإِنَّ لَكَ بِكُلِّ سَيِّئَةٍ حَسَنَةً، فَيَقُولُ: يَا رَبِّ عَمِلْتُ أَشْيَاءَ لَا أَرَاهَا ههُنَا»
(I know the last person who will be brought forth from Hell, and the last person who will enter Paradise. A man will be brought and it will be said, "Take away his major sins and ask him about his minor sins." So it will be said to him: "On such and such a day, you did such and such, and on such and such a day, you did such and such." He will say, "Yes, and he will not be able to deny anything." Then it will be said to him: "For every evil deed you now have one good merit." He will say: "O Lord, I did things that I do not see here.") He (Abu Dharr) said: "And the Messenger of Allah ﷺ smiled so broadly that his molars could be seen." Muslim recorded it. Ibn Abi Hatim recorded that Abu Jabir heard Makhul say, "A very old man with sunken eyes came and said, `O Messenger of Allah, a man betrayed others and did immoral deeds, and there was no evil deed which he did not do. If (his sins) were to be distributed among the whole of mankind, they would all be doomed. Is there any repentance for him" The Messenger of Allah ﷺ said:
«أَأَسْلَمْتَ؟»
(Have you become Muslim) He said, "As for me, I bear witness that there is no God but Allah Alone, with no partner or associate, and that Muhammad ﷺ is His servant and Messenger." The Prophet said:
«فَإِنَّ اللهَ غَافِرٌ لَكَ مَا كُنْتَ كَذَلِكَ، وَمُبَدِّلُ سَيِّئَاتِكَ حَسَنَات»
(Allah will forgive you for whatever you have done like that, and will replace your evil deeds with good merits.) The man said: "O Messenger of Allah, even my betrayals and immoral actions" The Prophet said:
«وَغَدَرَاتُكَ وَفَجَرَاتُك»
(Even your betrayals and immoral actions.) "The man went away saying `La ilaha illallah' and `Allahu Akbar."' Allah tells us how His mercy extends to all His creatrues, and that whoever among them repents to Him, He will accept his repentance for any sin, great or small. Allah says:
وَمَن تَابَ وَعَمِلَ صَـلِحاً فَإِنَّهُ يَتُوبُ إِلَى اللَّهِ مَتاباً
(And whosoever repents and does righteous good deeds; then indeed he has repented to Allah Mataba.) meaning, Allah will accept his repentance. This is like the Ayat:
وَمَن يَعْمَلْ سُوءاً أَوْ يَظْلِمْ نَفْسَهُ ثُمَّ يَسْتَغْفِرِ اللَّهَ يَجِدِ اللَّهَ غَفُوراً رَّحِيماً
(And whoever does evil or wrongs himself but afterwards seeks Allah's forgiveness, he will find Allah Oft-Forgiving, Most Merciful) (4:110).
أَلَمْ يَعْلَمُواْ أَنَّ اللَّهَ هُوَ يَقْبَلُ التَّوْبَةَ عَنْ عِبَادِهِ
(Know they not that Allah accepts repentance from His servants...) (9:104).
قُلْ يعِبَادِىَ الَّذِينَ أَسْرَفُواْ عَلَى أَنفُسِهِمْ لاَ تَقْنَطُواْ مِن رَّحْمَةِ اللَّهِ
(Say: "O My servants who have transgressed against themselves! Despair not of the mercy of Allah.") (39:53) - for those who repent to Him.