Imam Baqir (peace be upon him): Zurara said: I heard Rabi'at al-Ra'y saying: "In my view, the aqra' that Allah has named in the Quran is only the state of purity between two menstruations, and not the menstruation itself." I went to Imam Baqir (peace be upon him) and told him what Rabi'a had said. The Imam said: "Rabi'a lies, and this is not his own opinion; rather, he heard it from Ali (peace be upon him)." I said to the Imam: "May Allah grant you well-being! Did Ali (peace be upon him) really hold this view?" The Imam replied: "Yes! Ali (peace be upon him) used to say: 'Qur' means the state of purity [from menstrual blood]. The blood gathers before the time of menstruation, and at the time of menstruation, it is discharged.'" I said to the Imam: "May Allah grant you well-being! What is the ruling regarding a man who divorces his wife in a state of purity [when she is not menstruating], without having intercourse with her, in the presence of two just witnesses?" The Imam replied: "When that woman sees the blood of the third menstruation, her waiting period has ended and it is lawful for her to marry." I said to the Imam: "The people of Iraq say that Ali (peace be upon him) held that as long as this woman has not performed the ghusl of the third menstruation, her former husband has the right to return to her." The Imam said: "They lie, and Ali (peace be upon him) used to say: 'When the woman sees the blood of the third menstruation, her waiting period has ended.'" Then in Rabi'a's narration it is reported: that man cannot return to his divorced wife, and qur' means the state of purity between two menstruations, and that woman cannot marry until she performs the ghusl of the third menstruation. So if you take this as the basis [that qur' means what lies between two menstruations], the aqra' (three purities) equals three months. So if that woman is among those whose menstruation is irregular, and who menstruates several times in one month and once in another, she must keep the waiting period of a mustahada woman, three months; and if she is among those who have regular menstruation and menstruates once each month, then between two menstruations for her is counted as one month, and that is the qur'.