Ka`b b. Al-Ashraf [skipping Ka`b's Jewish tribal affiliations], when he heard the news [of the polytheists killed by Mohammed's troops at a recent battle] said, "Is it true? Did Muhammad actually kill these whom these two men mention (i.e. Zayd and `Abdullah b. Rawaha). These are the nobles of the Arabs and kingly men; by God, if Muhammad has slain these people 'twere better to be dead than alive." [translator's note: literally, the inside of the earth is better than the outside]
When the enemy of God [by which they mean the Jewish man Ka`b who objected to his polytheist friends being killed by Muslims] became certain that the news was true he left town and went to Mecca ... [skipping details on where he stayed, and his poem of lament for the dead in which he praises their generosity and help to the homeless, plus other poems by other people, and Ka'b's follow-up poem on the increasing hostility and dangerousness of those who had converted to Islam].
Then [wake up, this is considered quite an insult by the Muslims] Ka`b returned to Medina and composed amatory verses about Ummu'l-Fad'l al-Harith. [It's longish, it's in the footnotes if you want to see it.]1 Then he composed amatory verses of an insulting nature about the Muslim women. The apostle [by which they mean Mohammed] said -- according to what `Abdullah b. al-Mughith b. Abu Burda told me -- "Who will rid me of Ibnu'l Ashraf?" [that means K`ab, who is son of Al-Ashraf] Muhammad b. Maslama, brother of the B. `Abdu'l-Asshal, said, "I will deal with him for you, O apostle of God, I will kill him." He [Mohammed] said, "Do so if you can." So Muhammad b. Maslama returned and waited for three days without food or drink, apart from what was absolutely necessary. When the apostle was told of this he summoned him and asked him why he had given up eating and drinking. He replied that he had given him an undertaking and he did not know whether he could fulfil it. The apostle said, "All that is incumbent on you is that you should try." He said, "O apostle of God, we shall have to tell lies." He [Mohammed] answered, "Say what you like, for you are free in this matter."
[The rest of the account relates how they succeeded in killing Ka`b by deceit and treachery.]
1 - Ka`b's poem about the woman in question, the only "amatory verses of an insulting nature" which are recorded in the account:
Are you off without stopping in the valley
And leaving Ummu'l-Fadl in Mecca?
Out would come what she bought from the peddlar of bottles
Henna and hair dye
What lies 'twist ankle and elbow is in motion
When she tries to stand and does not
Like Umm Hakim when she was with us
The link between us firm and not to be cut.
She is one of the B. `Amir who bewitches the heart
And if she wished she could cure my sickness.
The glory of women and of a people is their father,
A people held in honor true to their oath.
Never did I see the sun rise at night till I saw her
Display herself to us in the darkness of the night.