All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
As to the question of one's having sexual intercourse with one's slave girl (bondmaid), we would like to state the following: The natural state of the person is that of freedom and not slavery. Slavery can only take place in limited reasons. As for a bondmaid, she is the one possessed by someone's right hand. A human being may be a right hand's possession by one of the following three ways:
1. Taking men or women prisoners from the non-Muslim enemies. The Muslim Imam (leader/ruler) here is given the option to either kill the men prisoners or take them as slaves, or take ransoms for their freedom, or set them free for nothing. As for women, they are not to be killed unless they fight.
2. A maid's child born to a man other than her master follows his mother in being a slave, whether or not his father was a slave.
3. Buying a bondmaid from her legal owner or taking her as a gift or by way of a will or through any way of property transfer from one person to another, are all legally recognized. Al-Muqawqis, king of Egypt, once gave the Prophet two bondmaids as a gift. He took one for himself as a wife and gave the other to Hassan Ibn Thabit . Knowing all these details, you have to take in mind that seeking enjoyment with a bondmaid by having sex with her or by its introductory things (such as kissing, embracing, fondling, etc.) are all disallowable unless she is legally and completely owned by a free man. Her owner must not have a partner in ownership, as it is possible that two men may share one bondmaid either by way of inheritance or otherwise. She must also be free from any objection that makes her forbidden to him, such as being his foster sister, or a bondmaid copulated by his son, grandson, or great-grandson, or by his father, grandfather or great- grandfather, or being married, or being a non-believer belonging to other than the People of the Book (Jews and Christians). If she met all these conditions, then he may have sex with her by means of right-hand possessing, and not by way of marriage contract. A bondmaid taken by her master for sexual intercourse is called 'Sariyyah' (bondmaid taken as a makeshift for wife in terms of coitus). If she gets pregnant from her master and gives birth – even if it is a miscarriage – then she would be called a 'child's mother' and would be set free directly after the demise of her master. As to the meaning of the Hadeeth, it is that this companion said that he used coitus interruption (meaning he had sex with her but ejaculated outside her vagina lest she became pregnant) in order for the prospective child not to be gibed being a bondmaid's son/daughter. The Jews at that time used to mistakenly say: "This practice (coitus interruption) is next to homicide since it would prevent the existence of an embryo". The Prophet refuted their allegation that the coitus interruption prevents pregnancy and proclaimed that it does never prevent pregnancy if Allah wills it to take place, and if He (Allah) does not decree it, then it is not homicide. So, what is meant by the Prophet's saying: “Once Allah wills to create it (embryo/child), you will never prevent it”; is that if Allah Almighty decrees to create a human being, He will definitely do that. And that one's water (sperm) may overwhelm the ejaculator and rush without his control no matter how he tries to curb it. So, this sperm may gush out unconsciously for Allah's pre-ordainment to be fulfilled.
Allah knows best.