Musnad Ahmad 1142:1

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from 'Abdullah ibn Ka'b ibn Malik, from his paternal uncle: That Ka'b ibn al-Ashraf used to satirize the Prophet, peace and blessings of Allah be upon him. So the Prophet, peace and blessings of Allah be upon him, ordered Sa'd ibn Mu'adh to send five men to him. They came to him while he was in the gathering of his people in al-'Awali. When he saw them, he was alarmed by them and said, "What has brought you?" They said, "We have come to you for a need." He said, "Let one of you draw near to me and tell me his need." One of them drew near to him and they said, "We have come to you to sell you some coats of mail of ours." He said, "By Allah, if you have done so, you have been in hardship since this man settled among you"—or he said, "among you." They made an appointment with him to come to him after a quiet part of the night. He said: So they came to him, and he stood up to go to them. His wife said to him, "These men have not come to you at this hour for anything you would like." He said, "They have told me their need." When he drew near to them, Abu 'Abs embraced him, and Muhammad ibn Maslamah struck him with the sword and stabbed him in his flank, and they killed him. When the Jews reached the morning, they went to the Prophet, peace and blessings of Allah be upon him, and said, "Our leader was killed by treachery." The Prophet, peace and blessings of Allah be upon him, reminded them of what he used to satirize him with in his poems and how he used to harm him. Then the Prophet, peace and blessings of Allah be upon him, invited them to write a document between him and them. He said: So that document was with 'Ali.