Is it permissible for Muslims to marry female captives (taken as spoils of war) without a legitimate Islamic contract, and was the marriage of the Messenger of Allah, peace and blessings be upon him, to Lady Safiyyah, may Allah be pleased with her, conducted with a contract or not?

The question comprises two parts:

The first: Cohabiting with captives. The Shari'ah permitted cohabiting with women through two means: a marriage contract for free women, and ownership by the right hand for slave women, in accordance with His, the Almighty’s, saying: (And those who guard their private parts Except from their wives or those their right hands possess, for indeed, they will not be blamed). There are regulations for establishing ownership by the right hand, and the default status for people is freedom.

The second: The Prophet’s, peace and blessings be upon him, marriage to Safiyyah bint Huyayy, may Allah be pleased with her. He freed her then married her with her consent, as reported in the Two Sahihs and other collections.