A confession to murder is valid and the heir of the victim is entitled to Qisas, but it is recommended to ask him to let him go

'Alqama b. Wa'il reported on the authority of his-father: While I was sitting in the company of Allah's Apostle ﷺ, a person came there dragging another one with the help of a strap and said: Allah's Messenger, this man has killed my brother. Messenger of Allah ﷺ said to him: Did you kill him? And the other man said: (In case he did not make a confession of this, I shall brine, a witness against him). He (the murderer) said: Yes, I have killed him. He (the Holy Prophet) said: Why did you kill him? He said: I and he won striking down the leaves of a tree and he abused me and enraged me, and to I struck his head with an axe and killed him, whereupon Messenger of Allah ﷺ said: Have you anything with you to pay blood-wit on your behalf? He said: I do not possess any property but this robe of mine and this axe of mine. He (the Holy, Prophet) said: Do you think your people will pay ransom for you? He said: I am more insignificant among my people than this (that I would not be able to get this benefit from my tribe). He (the Holy Prophet) threw the strap towards him (the claimant of the blood-wit) saying: Take away your man. The man took him away, and as he returned, Messenger of Allah ﷺ said: If he kills him, he will be like him. He returned and said: Allah's Messenger, it has reached me that you have said that" If he killed him, he would be like him." I caught hold of him according to your command, whereupon Messenger of Allah ﷺ said: Don't you like that he should take upon him (the burden) of your sin and the sin of your companion (your brother)? He said: Allah's Apostle, why not? The Messenger of Allah (may peace be. upon him) said: If it is so, then let it be. He threw away the strap (around the offender) and set him free.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا أَبُو يُونُسَ، عَنْ سِمَاكِ بْنِ، حَرْبٍ أَنَّ عَلْقَمَةَ بْنَ وَائِلٍ، حَدَّثَهُ أَنَّ أَبَاهُ حَدَّثَهُ قَالَ إِنِّي لَقَاعِدٌ مَعَ النَّبِيِّ ﷺ إِذْ جَاءَ رَجُلٌ يَقُودُ آخَرَ بِنِسْعَةٍ فَقَالَ يَا رَسُولَ اللَّهِ هَذَا قَتَلَ أَخِي . فَقَالَ رَسُولُ اللَّهِ ﷺ " أَقَتَلْتَهُ " . فَقَالَ إِنَّهُ لَوْ لَمْ يَعْتَرِفْ أَقَمْتُ عَلَيْهِ الْبَيِّنَةَ . قَالَ نَعَمْ . قَتَلْتُهُ قَالَ " كَيْفَ قَتَلْتَهُ " . قَالَ كُنْتُ أَنَا وَهُوَ نَخْتَبِطُ مِنْ شَجَرَةٍ فَسَبَّنِي فَأَغْضَبَنِي فَضَرَبْتُهُ بِالْفَأْسِ عَلَى قَرْنِهِ فَقَتَلْتُهُ . فَقَالَ لَهُ النَّبِيُّ ﷺ " هَلْ لَكَ مِنْ شَىْءٍ تُؤَدِّيهِ عَنْ نَفْسِكَ " . قَالَ مَا لِي مَالٌ إِلاَّ كِسَائِي وَفَأْسِي . قَالَ " فَتَرَى قَوْمَكَ يَشْتَرُونَكَ " . قَالَ أَنَا أَهْوَنُ عَلَى قَوْمِي مِنْ ذَاكَ . فَرَمَى إِلَيْهِ بِنِسْعَتِهِ . وَقَالَ " دُونَكَ صَاحِبَكَ " . فَانْطَلَقَ بِهِ الرَّجُلُ فَلَمَّا وَلَّى قَالَ رَسُولُ اللَّهِ ﷺ " إِنْ قَتَلَهُ فَهُوَ مِثْلُهُ " . فَرَجَعَ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّهُ بَلَغَنِي أَنَّكَ قُلْتَ " إِنْ قَتَلَهُ فَهُوَ مِثْلُهُ " . وَأَخَذْتُهُ بِأَمْرِكَ . فَقَالَ رَسُولُ اللَّهِ ﷺ " أَمَا تُرِيدُ أَنْ يَبُوءَ بِإِثْمِكَ وَإِثْمِ صَاحِبِكَ " . قَالَ يَا نَبِيَّ اللَّهِ - لَعَلَّهُ قَالَ - بَلَى . قَالَ " فَإِنَّ ذَاكَ كَذَاكَ " . قَالَ فَرَمَى بِنِسْعَتِهِ وَخَلَّى سَبِيلَهُ .