No they can't have sex without marriage , I know about quran so my evidence will be from the quran which never changed
any one can corrupt hadith
Allah says in
Quran 4:25
"And whoever among you cannot [find] the means to marry free, believing women, then [he may marry] from those whom your right hands possess of believing slave girls. And Allah is most knowing about your faith. You [believers] are of one another. So marry them with the permission of their people and give them their due compensation according to what is acceptable. [They should be] chaste, neither [of] those who commit unlawful intercourse randomly nor those who take [secret] lovers. But once they are sheltered in marriage, if they should commit adultery, then for them is half the punishment for free [unmarried] women. This [allowance] is for him among you who fears sin, but to be patient is better for you. And Allah is Forgiving and Merciful."
he also says in
Quran 24:32
"And marry the unmarried among you and the righteous among your male slaves and female slaves. If they should be poor, Allah will enrich them from His bounty, and Allah is all-Encompassing and Knowing"
also what Ottoman Turks did , by slaving people in wars was wrong
tallah says in quran 47:4
So when you meet those who disbelieve [in battle], strike [their] necks until, when you have inflicted slaughter upon them, then secure their bonds, and either [confer] favor afterwards or ransom [them] until the war lays down its burdens. That [is the command]. And if Allah had willed, He could have taken vengeance upon them [Himself], but [He ordered armed struggle] to test some of you by means of others. And those who are killed in the cause of Allah - never will He waste their deeds.
we can't slave people from another countries if they "prisoner" our people we have to do the same , when war ends , Either we ransom them { exchange with our people that are in the hands of enemies people , or set them free