Kinana ibn al-Rabi' ibn Abu al-Huqayq was a leader/chief of the Jews of Khaybar and husband of Safiyah, who later became one of Muhammad's wives. One source relates that Kinana and Safiyah had only been married one day prior to his death.
Torture and Beheading of Kinana
Kinana b. al-Rabi', who had the custody of the treasure of the B. al-Nadir, was brought to the apostle who asked him about it. He denied that he knew where it was. A Jew came (Tabari says "was brought") to the apostle and said that he had seen Kinana going round a certain ruin every morning early. When the apostle said to Kinana, 'Do you know that if we find you have it I shall kill you?' he said Yes. The apostle gave orders that the ruin was to be excavated and some of the treasure was found. When he asked him about the rest he refused to produce it, so the apostle gave ordrs to al-Zubayr b. al-'Awwam, 'Torture him until you extract what he has,' so he kindled a fire with flint and steel on his chest until he was nearly dead. Then the apostle delivered him to Muhammad b. Maslama and he struck off his head in revenge for his brother Mahmud.
Kinanah b. al-Rabi b. al-Huqyaq who had the treasure of B. Nadir was brought to the Messenger of God, who questioned him; but he denied knowing where it was. Then the messenger of God was brought a Jew who said to him, “I have seen Kinanah walk around this ruin every morning.” The Messenger of God said to Kinanah: “What do you say? If we find it in your possession, I will kill you.” “All right,” he answered. The Messenger of God commanded that the ruin should be dug up, and some of the treasure was extracted from it. Then he asked him for the rest of it. Kinanah refused to surrender it; so the Messenger of God gave orders concerning him to al-Zubayr b. al-‘Awwam, saying, “torture him until you root out what he has.” Al-Zubayr kept twirling his firestick in his breast until Kinanah almost expired; then the Messenger of God gave him to Muhammad b. Maslamah, who beheaded him to avenge his brother Mahmud b. Maslamah.”
Tabari vol. 8, p.123
After this defeat, the fortress of Camuss surrendered, on condition that the inhabitants were free to leave the country, but that they should give up all their property to the conqueror. With the rest, came forth Kinana, chief of the Jews of Kheibar, and his cousin. Mahomet accused them both of keeping back, in contravention of the compact, a portion of their riches, especially the treasures of the Bani Nadhir, which Kinana had obtained as a marriage portion with his wife Safia, the daughter of Huwey who perished in the slaughter of the Bani Coreitza.
"Where are the vessels of gold," he asked, "which ye used to lend to the people of Mecca?" They protested that they no longer possessed them.
"If ye conceal anything from me," continued Mahomet, "and should I gain knowledge of it, then your lives and the lives of your families shall be at my disposal." They answered that it should be so.
A traitorous Jew, having divulged to Mahomet the place in which a part of their wealth was deposited, he sent and fetched it. On the discovery of this attempt at imposition, Kinana was subjected to cruel torture,--"fire being placed upon his breast till his breath had almost departed,"--in the hope that he would confess where the rest of his treasures were concealed. Mahomet then gave command, and the heads of the two chiefs were severed from their bodies.
The claim that Kinana was beheaded for the death of Mahmud
Angry over the death of his brother, Muhammad b. Maslamah asked Muhammad for permission to fight and kill Marhab. He succeeded. So why then was Kinana killed for the death of Mahmud b. Maslamah?
At one stage in the campaign, Marhab came out of one of the fortresses fully covered with his military attire and singing the following verses: "Khaybar knows that I am Marhab, that I am an experienced hero fully prepared for war. I deal blows to my enemies and I strike them. Even the lions I face with drawn sword. The ground I hold is unassailable. Even the most experienced in war dares not approach it. "
Muhammad asked his companions, "Who will rise to meet him?"
Muhammad ibn Maslamah rose and said, "Send me, O Prophet of God. For I am angry and bereaved, who lost his brother yesterday." The Prophet permitted him and he sprang to meet Marhab. The pair fought valiantly and, at one stage, Marhab almost killed the Muslim. Ibn Maslamah, however, intercepted the falling sword with his shield which bent under its weight and was cut so that the sword could not be pulled out and disengaged. Muhammad ibn Maslamah seized the opportunity and gave Marhab a fatal blow.