for a captured slave woman or any other slave woman before marital relations, and it also sets out the period of istibrāʾ required for those captives who are pregnant or menstruating.

As for a slave woman who has ceased to menstruate, or one who is still pre-pubescent, their istibrāʾ is fulfilled by the passing of one lunar month, because a month substitutes for a single menstrual cycle in matters of waiting periods.

The rationale behind requiring istibrāʾ before intercourse is made clear by the Prophet’s words: “Whoever believes in Allah and the Last Day must not water another man’s crop with his own seed.” Thus the purpose of istibrāʾ is to prevent the mingling of seminal fluids and any confusion of lineage.