Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Who will kill Ka'b bin al-Ashraf? He has harmed Allah and His Messenger (peace and blessings be upon him)." Muhammad bin Maslamah (may Allah be pleased with him) said: O Messenger of Allah (peace and blessings be upon him)! Would you (peace and blessings be upon him) like me to kill him? He (peace and blessings be upon him) said: "Yes." He said: O Messenger of Allah (peace and blessings be upon him)! I will kill him, but permit me (peace and blessings be upon him) to say some things. He (peace and blessings be upon him) said: "Say them." Muhammad bin Maslamah (may Allah be pleased with him) came to him and said: This man (meaning Muhammad, peace and blessings be upon him) has taken charity from us and been hard on us, and we have grown weary of him. When the wicked man heard these words, he said: Moreover, by Allah, you will certainly grow weary of him, and I knew that your affair would come to this. He said: We cannot abandon him until we see what he does, and we dislike leaving him after having followed him until we see where his affair ends up. I have come to you so that you may lend me some dates. He said: All right, but pledge your women to me. Muhammad bin Maslamah (may Allah be pleased with him) said: You are the most handsome of the Arabs; should we pledge our women to you? He said: Then pledge your children. Muhammad bin Maslamah (may Allah be pleased with him) said: People would taunt our children that we pledged them for one or two wasqs, and sometimes our children would be reviled: This is the one who was pledged for one or two wasqs. He said: What will you pledge to me? Muhammad bin Maslamah (may Allah be pleased with him) said: We will pledge our weapons to you. He said: Agreed. He arranged that he would come to him. Muhammad bin Maslamah (may Allah be pleased with him) went back to his companions, and with him came Abu Na'ilah (may Allah be pleased with him), who was Ka'b's foster brother, and two other men. He said: I will get a firm hold of his head; when I put my hand into his hair, attack him. They came one night, and Muhammad bin Maslamah (may Allah be pleased with him) told his companions to stand in the shade of the date palms. Muhammad bin Maslamah (may Allah be pleased with him) came and called out: O Abu al-Ashraf! His wife said: Where are you going at this hour? He said: It is Muhammad bin Maslamah (may Allah be pleased with him) and my brother Abu Na'ilah (may Allah be pleased with him). He came down wrapped in a single garment, giving off the scent of perfume. Muhammad bin Maslamah (may Allah be pleased with him) said: How handsome your body is, and how fine your scent! He said: The daughter of so-and-so is married to me, and she is the most fragrant of the Arabs. Muhammad (bin Maslamah, may Allah be pleased with him) said: Will you permit me to smell it? He said: Yes. So he put his hand into his hair, then said: Will you permit me to let my companions smell it? He said: Yes. So he put his hand into his hair and let his companions smell the scent. Then he put his hand into his hair a second time, until Ka'b felt at ease with him; then he seized the hair of his head and forelock firmly and said to his companions: Attack the enemy of Allah! They came out and killed him, and then they came and informed the Messenger of Allah (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18102