Volume 3, Book 49, Number 865 :
Narrated by Sahl bin Abu Hathma (radiallaahu `anhu)
Abdullah bin Sahl and Muhaiyisa bin Mas’ud bin Zaid (radiallaahu `anhumaa) went to Khaibar when it had a peace treaty (with the Muslims).
Here’s the complete story (narrations found elsewhere in Bukhari):
Volume 4, Book 53, Number 398 :
Narrated by Sahl bin Abi Hathma (radiallaahu `anhu)
‘Abdullah bin Sahl and Muhaiyisa bin Mas’ud bin Zaid (radiallaahu `anhumaa) set out to Khaibar, the inhabitants of which had a peace treaty with the Muslims at that time. They parted and later on Muhaiyisa came upon ‘Abdullah bin Sahl (radiallaahu `anhu) and found him murdered agitating in his blood. He buried him and returned to Medina. ‘Abdur Rahman bin Sahl, Muhaiyisa and Huwaiuisa (radiallaahu `anhum), the sons of Mas’ud came to the Prophet (sallallaahu `alayhi wasallam) and ‘Abdur Rahman (radiallaahu `anhu) intended to talk, but the Prophet (sallallaahu `alayhi wasallam) said (to him), “Let the eldest of you speak.” as ‘Abdur-Rahman was the youngest:. ‘Abdur-Rahman kept silent and the other two spoke. The Prophet said, “If you swear as to who has committed the murder, you will have the right to take your right from the murderer.” They said, “How should we swear if we did not witness the murder or see the murderer?” The Prophet (sallallaahu `alayhi wasallam) said, “Then the Jews can clear themselves from the charge by taking Alaska (an oath taken by men that it was not they who committed the murder).” The!y said, “How should we believe in the oaths of infidels?” So, the Prophet (sallallaahu `alayhi wasallam) himself paid the blood money (of ‘Abdullah).
Volume 9, Book 83, Number 36:
Narrated by Sahl bin Abi Hathma (radiallaahu `anhu)
(a man from the Ansar) That a number of people from his tribe went to Khaibar and dispersed, and then they found one of them murdered. They said to the people with whom the corpse had been found, “You have killed our companion!” Those people said, “Neither have we killed him, nor do we know his killer.” The bereaved group went to the Prophet (sallallaahu `alayhi wasallam) and said, “O Allah’s Apostle! We went to Khaibar and found one of us murdered.” The Prophet (sallallaahu `alayhi wasallam) said, “Let the older among you come forward and speak.” Then the Prophet (sallallaahu `alayhi wasallam) said, to them, “Bring your proof against the killer.” They said “We have no proof.” The Prophet (sallallaahu `alayhi wasallam) said, “Then they (the defendants) will take an oath.” They said, “We do not accept the oaths of the Jews.” Allah’s Apostle (sallallaahu `alayhi wasallam) did not like that the Blood-money of the killed one be lost without compensation, so he paid one-hundred camels out of the camels of Zakat (to the relatives of the deceased) as Diya (Blood-money).
Since there was no proof, Prophet (sallallaahu `alayhi wasallam) could not take an action against the Jews without getting an oath from them. But the bereaved ones were not going to accept the oath of Jews assuming they’d repeat the same story: “Neither have we killed him, nor do we know his killer”. So Prophet (sallallaahu `alayhi wasallam) arranged for the blood money to close the case.
Allaah, may He be exalted, says (interpretation of the meaning):
“O you who believe! Al-Qisaas (the Law of Equality in punishment) is prescribed for you in case of murder: the free for the free, the slave for the slave, and the female for the female. But if the killer is forgiven by the brother (or the relatives) of the killed against blood money, then adhering to it with fairness and payment of the blood money to the heir should be made in fairness. This is an alleviation and a mercy from your Lord. So after this whoever transgresses the limits (i.e. kills the killer after taking the blood money), he shall have a painful torment”
The great scholar ‘Abd al-Rahmaan al-Sa’di said in his Tafseer: Allaah reminds His believing slaves that He has enjoined qisaas upon them in the case of murder, i.e., there should be equal recompense in that, and that the killer should be killed in the way in which he killed his victim, so as to establish justice and fairness among people. End quote.
Qisaas by killing the killer can only be in cases of deliberate killing, according to scholarly consensus. Ibn Qudaamah said in al-Mughni (8/214): The scholars are unanimously agreed that qisaas is not required except in the case of deliberate killing, and we do not know of any difference of opinion with regard to qisaas being required for deliberate killing if all conditions are met. This is indicated by the general meaning of the verses and reports. Allaah says (interpretation of the meaning):
“And whoever is killed wrongfully (Mazlooman intentionally with hostility and oppression and not by mistake), We have given his heir the authority [to demand Qisaas, __Law of Equality in punishment __or to forgive, or to take Diyah (blood money)]. But let him not exceed limits in the matter of taking life (i.e. he should not kill except the killer)” [al-Isra’ 17:33]
“Al-Qisaas (the Law of Equality in punishment) is prescribed for you in case of murder”
“And there is (a saving of) life for you in Al-Qisaas”
What is meant – and Allaah knows best – is that the requirement of qisaas deters the one who wants to kill from doing do, out of compassion towards himself so that he will not killed, and so that the one whom he wanted to kill will remain alive. And it was said that the killer would generate enmity between himself and the tribe of the one whom he killed, so he wants to kill them for fear of them and they want to kill him and his tribe in revenge. If he is executed as a punishment according to sharee’ah, that will prevent the reason for fighting between the two tribes. And Allaah says (interpretation of the meaning):
“And We ordained therein for them: Life for life, eye for eye”
The Prophet (peace and blessings of Allaah be upon him) said: “If a person’s relative is killed, he has the choice of two options: either (the killer) may be killed or the fidyah (ransom, blood money) may be paid.” Agreed upon. Abu Shurayh al-Khuzaa’i said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever is killed or is wounded, has the choice of three things, and if he wants the fourth then restrain him. He may kill (the killer), or forgive him, or take the diyah (blood money). Narrated by Abu Dawood. According to another version: “Whoever has a relative killed after what I have said, his family has two options: to accept the diyah or kill (the killer).” And he (peace and blessings of Allaah be upon him) said: “There is qisaas for deliberate killing, unless the heir of the slain lets him off.” End quote.
There was no difference of opinion among the scholars that it is valid for the heirs of the victim to forego qisaas and accept the diyah. This is what is indicated by the ahaadeeth quoted above.
In that case, the killer may be set free and he should be obliged to pay the diyah.
Taken from IslamQA