It is not permissible for a man to have intercourse with anyone except his wife or his female slave (concubine). A wife becomes permissible after shar’i marriage and a concubine becomes permissible to the man who owns her. She may originally be a prisoner of war, and a Muslim may obtain a concubine from the ruler or commander if he took part in fighting in jihad, or if he buys her from her owner. She becomes permissible for him by virtue of his ownership after it is established that she is not pregnant by waiting for one menstrual cycle, or until she has given birth if she is pregnant. 

Allaah says (interpretation of the meaning): 

“And those who guard their chastity (i.e. private parts, from illegal sexual acts)

6. Except from their wives or (the slaves) that their right hands possess, ـــ for then, they are free from blame”

[al-Mu’minoon 23:5-6]

It was narrated that Abu Sa’eed al-Khudri said: The Prophet (peace and blessings of Allaah be upon him) said, concerning the prisoners of Awtaas: “Do not have intercourse with a pregnant woman until she gives birth, or with one who is not pregnant until she has menstruated once.” Narrated by Abu Dawood, 2157. This hadeeth was classed as saheeh by Shaykh al-Albaani in Irwa’ al-Ghaleel, 187. 

In the answer to question no. 10382 we have stated that Islam permits a man to have intercourse with his slave woman whether he has one or more wives or he is not married. 

In the answers to questions no. 5707 and 12562 it states that female prisoners of war may be distributed by the commander in jihad, because he has the choice of either distributing them, or ransoming them or setting them free.