Allah's saying:

[وَلاَ تُكْرِهُواْ فَتَيَـتِكُمْ عَلَى الْبِغَآءِ]

(And force not your slave-girls to prostitution...) Among the people of the Jahiliyyah, there were some who, if he had a slave-girl, he would send her out to commit Zina and would charge money for that, which he would take from her every time. When Islam came, Allah forbade the believers to do that. The reason why this Ayah was revealed, according to the reports of a number of earlier and later scholars of Tafsir, had to do with `Abdullah bin Ubayy bin Salul. He had slave-girls whom he used to force into prostitution so that he could take their earnings and because he wanted them to have children which would enhance his status, or so he claimed.