to count two complete states of purity and part of a third, which runs counter to the plain wording of the verse.
The stronger position is that the qurūʾ are the actual periods of menstruation, and Allah knows best.
As for ḥadith no. 970, it shows that the final limit of divorce for a slave-woman is two pronouncements. Its general phrasing further indicates that this applies whether the divorcing husband is free or a slave, because the criterion for the number of divorces is the woman who is being divorced. This is the view of the Ḥanafī school, and it is related from ʿAlī, Ibn Masʿūd, al-Ḥasan, Ibn Sīrīn, ʿIkrimah, al-Zuhrī, Ḥammād, and al-Thawrī, their proof being the very ḥadith at hand.
Those who tie the ruling to the husband maintain that a slave-woman may be divorced only twice in every situation, whether she is married to a free man or a slave. This is the opinion of the three imams—Mālik, al-Shāfiʿī, and Aḥmad—as well as Isḥāq and Ibn al-Mundhir, and it is also reported from ʿUmar, ʿUthmān, Zayd ibn Thābit, Ibn ʿAbbās, and Saʿīd ibn al-Musayyib.
Their evidence is that Allah addressed the command of divorce to the man, so the ruling, in their view, follows him.
The ḥadith in this chapter is transmitted through Muẓāhir ibn Aslam; Abū Dāwūd declared his ḥadith to be munkar (irregular).
Even if it were deemed authentic, its intent would be the case in which the slave-woman’s husband is himself a slave. Al-Dāraquṭnī explicitly recorded it in a marfūʿ report from ʿĀʾishah: “The divorce of a slave is two; she is not lawful for him thereafter until she marries another husband, and the waiting period of a slave-woman is two menstruations.” This statement is conclusive on the matter.
With respect to the waiting period of a slave-woman, the consensus is that it is two menstrual cycles. This is narrated from ʿUmar, his son, and ʿAlī—may Allah be pleased with them—and no Companion is known to have disagreed, so it constitutes a consensus.
Ibn Hubayrah said: “They unanimously agreed that the waiting period of a slave-woman, when reckoned by qurūʾ, is two qurʾs, and they concurred that her waiting period is counted in qurūʾ if she menstruates.”