“with his female slaves,” meaning, those whom he owns. Thus, a master who has female slaves may marry them off without their permission, even if they are adults, because he owns them outright. Evidence for this is the saying of Allah, Exalted is He:
“Do not compel your slave girls to prostitution if they desire chastity.” [al-Nur 24:33]
Its implied meaning is that compelling them to something other than prostitution—such as a valid marriage—is unobjectionable. And this is indeed the case. Allah, Exalted is He, also says:
“Whoever among you cannot afford to marry free believing women, then let him marry from the believing slave women whom your right hands possess. Allah knows best the reality of your faith; you are of one another. So marry them with the permission of their owners.” [al-Nisa’ 4:25]
Their owners, then, are those who marry them off. The master possesses his female slave completely: both her person and her usufruct. Thus, if she were to say, “Marry me off,” and he replied, “No; I wish to take you as my concubine,” we would not compel him to marry her off. The owner may marry off his female slaves whether they consent or not. Yet, in every case, he must not impose hardship upon them or marry them to someone they do not accept.
His words, “like the master with his female slaves”: is it permissible to apply the term “master” to an owner?
The answer is that the term “master,” when used independently—not specifically in the sense of an owner—is common, as in the story of Joseph, peace be upon him: “They found her master at the door.” [Yusuf 12:25] Likewise, the Prophet, peace and blessings be upon him, said, “I am the leader of the children of Adam” (1), and he said, “Stand for your leader” (2).