Musnad Abu Ya'la al-Mawsili 5:18

Zuhayr narrated to us, Muhammad ibn al-Hasan al-Madani narrated to us, Umm 'Urwah narrated to me, from her father, from her grandfather al-Zubayr, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) left his women behind in Medina, he left them in Fari'. Among them was Safiyyah bint 'Abd al-Muttalib, and he left Hassan ibn Thabit among them. A man from the polytheists approached to enter upon them. Safiyyah said to Hassan, "There is a man at your place." Hassan became cowardly and refused her. Safiyyah took the sword and struck the polytheist with it until she killed him. The Messenger of Allah (peace and blessings of Allah be upon him) was informed of that, so he assigned a share for Safiyyah just as he used to assign for the men.