A man's ownership of his unmarried slave-girl gave him an exclusive right to have sex with her under the condition that he could not sell her to others (in order to prevent prostitution of slaves). A man could own a limitless number of concubines, but could not have access to the slave-girls owned by his wife. Marriage between the master and his concubine was only possible if she was granted free status first. To avoid pregnancies, the master had the right to practice coitus interruptus. The birth of progeny would change the legal status of the concubine to that of "umm al-walad" ("mother of the child"); as such, the concubine could not then be sold. On the (lawful) death of her master, she would automatically acquire free status and her children would be considered free and legitimate. Surah Al-Muminun (23:6) and Surah Al-Maarij (70:30) both, in identical wording, draw a distinction between spouses and "those whom one's right hands possess" (female slaves), saying " أَزْوَاجِهِمْ أَوْ مَا مَلَكَتْ أَيْمَانُهُمْ" (literally, "their spouses or what their right hands possess"), while clarifying that sexual intercourse with either is permissible. The purchase of female slaves for sex was lawful from the perspective of Islamic law, and this was the most common motive for the purchase of slaves throughout Islamic history. One rationale given for recognition of concubinage in Islam is that "it satisfied the sexual desire of the female slaves and thereby prevented the spread of immorality in the Muslim community." Most schools restrict concubinage to a relationship where the female slave is required to be monogamous to her master (though the master's monogamy to her is not required), but according to Sikainga, "in reality, however, female slaves in many Muslim societies were prey for [male] members of their owners' household, their [owner's male] neighbors, and their [owner's male] guests." It is also considered a cultural taboo as a result according to which it was banned in numerous Islamic Empires and is out of favor in modern day Muslim countries. The practice has recently seen a revival among terrorist circles like the ISIS and Daesh. The history of slavery in Islamic states and of sexual relations with slaves, was the "responsibility of Muslims, and not of the Quran", according to Parwez, as quoted by Clarence-Smith.