Accepting what a woman says about the beginning and end of a period

Firstly: 

In the answer to question no. 72417 we have stated that the scholars differed as to whether the divorce of a menstruating woman counts as valid, but the correct view is that it does not count. 

Secondly: 

The word of a woman concerning the start and end of her period, and other matters of which men have no knowledge, is to be accepted because she is to be trusted with that. Al-Shaafa’i (may Allaah have mercy on him) said: “Sufyaan narrated to us from ‘Amr ibn Dinar that ‘Ubayd ibn ‘Umayr said: A woman is to be trusted with regard to personal matters.” End quote from al-Umm, 5/225. 

The fact that a woman’s words concerning such matters is to be accepted is indicated by the verse in which Allaah says (interpretation of the meaning): 

“and it is not lawful for them to conceal what Allaah has created in their wombs, if they believe in Allaah and the Last Day”

[al-Baqarah 2:228]

al-Jassaas (may Allaah have mercy on him) said: The fact that Allaah commands women not to conceal (what He has created in their wombs) indicates that what a woman says about menstruation or the absence thereof is to be accepted, and the same applies to pregnancy too, because these are both things that Allaah has created in her womb. If a woman’s word concerning these matters were not acceptable, then He would not have warned woman not to conceal them. Thus it is established that if a woman says, “I am menstruating”, it is not permissible for her husband to have intercourse with her, and when she says, “My period is over,” it is permissible for him to have intercourse with her. By the same token our companions said that if he says to her, “You are divorced when you get your period,” and she says, “I have got my period,” then she is divorced and her words are like proof. End quote from Ahkaam al-Qur’aan, 1/506 

Al-Sa’di (may Allaah have mercy on him) said (p. 102): 

This indicates that what a woman says about matters that concern her and of which no one else can have any knowledge, such as pregnancy, menstruation, etc., is to be accepted. End quote. 

It says in Mu’een al-Hukkaam  (p. 95): Concerning passing judgement on the basis of the statement of one woman in matters of which women alone have knowledge: that is matters concerning which only women have knowledge, such as childbirth, whether a woman is a virgin or not, menstruation, pregnancy, miscarriage, faults of free woman and slave woman and everything that is beneath their garments. The point here is that because these are matters to which men are not privy and they have no knowledge of them, then in these cases the testimony of women is regarded as equal to that of men, because of necessity. End quote. 

In order for a woman’s words concerning these matters to be accepted, her claim that a period has begun or ended must come at a time when that is possible; if she makes such a claim at a time when it is not possible, then her words should not be accepted. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: 

Among the things that we learn from this verse are the following: 

What a woman says concerning her ‘iddah is to be accepted, because Allaah , may He be exalted, says: “and it is not lawful for them to conceal what Allaah has created in their wombs” [al-Baqarah 2:228]. The point here is that Allaah has made their words carry weight; if they did not carry weight, then their concealing (what has been created in their wombs) would not have any effect. So if she says that her ‘iddah has ended, and that is within the possible time frame, then she should be believed, and she is to be trusted with regard to that. But if she claims that her ‘iddah has ended within an impossible time frame, then her words are to be rejected, because one of the conditions of a claim being accepted is that it should be something that is possible, and a claim of something that is impossible should not be listened to at all. End quote.  

Tafseer Soorat al-Baqarah, p. 102 

See also: al-Mughni, 7/158; al-Fawaakih al-Dawaani, 2/34 

And Allaah knows best.