Praise be to Allah.
Firstly: when a woman menstruates, her period is over when the blood stops, regardless of whether the blood was a lot or a little. Many fuqahaa’ stated that the shortest length of a woman’s period is a day and a night, and the longest is fifteen days.
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said there was no minimum or maximum for it; when the bleeding is present with its distinct qualities, this is menstruation, whether it is a little or a lot. He said:
“Menstruation (al-hayd): Allaah has attached numerous rulings to it in the Qur’aan and Sunnah, but He did not state the shortest or longest length (of a menstrual period), or the length of the period of tahaarah between two menstrual periods, even though the need to know that exists.”
Then he said:
“Some of the scholars defined a maximum and minimum, but they differed concerning that, and some stated a maximum length without defining a minimum. The third view is most correct, which states that there is no minimum or maximum.”
(Majmoo’ al-Fataawaa, 19/237)
Secondly: There is a kind of bleeding which is called “al-istihaadah”, [irregular, non-menstrual vaginal bleeding] which is different from menstrual bleeding. It is governed by rulings which differ from those governing menstruation. This blood (istihaadah) may be distinguished from the blood of menstruation by the following:
Colour: menstrual blood is black [dark red] whilst the blood of istihaadah is red.
Consistency: menstrual blood is thick and heavy, whilst the blood of istihaadah is thin.
Smell: menstrual blood has an offensive odour whilst the blood of istihaadah does not, because it comes from an ordinary vein.
Clotting: menstrual blood does not clot when it comes out of the body whilst the blood of istihaadah does clot because it comes from a vein.
These are the characteristics of menstrual blood, so if this description fits the blood that is coming out, it is hayd (menstruation); ghusl is waajib (obligatory) and this blood is naajis (impure), but ghusl is not required in the case of istihaadah.
When a woman has her period she is not allowed to pray, but when the bleeding is istihaadah, that is not the case. But she has to be careful and has to do wudoo’ for each prayer if the flow of blood continues to the next prayer. If blood comes out whilst she is praying, it does not matter.
Thirdly; a woman can know that her period has ended by two things:
The white discharge which comes from the womb to show that the period is over.
Complete dryness, if a woman does not have this white discharge. In this case she can find out if her period has ended by inserting a piece of white cotton or something similar into the place where the blood comes from; if it comes out clean, then her period is over and she has to do ghusl and pray. If the cloth comes out red, yellow or brown, she should not pray.
The women used to send small containers in which were these cloths with traces of yellow on them to ‘Aa’ishah, and she would say, “Do not hasten until you see the white discharge.”(Narrated by al-Bukhaari mu’allaqan. Kitaab al-Hayd, Baab iqbaal al-muhayd wa idbaarihi. Also by Maalik, 130).
But if there is a yellow or brownish discharge when a woman does not have her period, this does not mean anything and she should not stop praying or do ghusl because of it, because it does not necessitate ghusl or cause janaabah (impurity).
Umm ‘Atiyyah (may Allaah be pleased with her) said: “We did not bother about any yellow or brownish discharge after a woman’s period was over.”(Narrated by Abu Dawood, 307. It was also narrated by al-Bukhaari, 320, but he did not mention “after a woman’s period was over.”)
“We did not bother about” means we did not think it was menstruation, but it is a naajis (impure) discharge which means that a woman has to wash it away and do wudoo’. But if the white discharge is immediately followed by a period, then it is part of the period.
Fourthly: if a woman believes that her period has ended, then she starts bleeding again, if the blood has the characteristics of menstrual blood as described above, then this is menstrual bleeding, otherwise it is istihaadah.
If it is the former, she should not pray. If it is the latter, she should be careful and do wudoo’ for each prayer, then pray.
Concerning the brownish discharge, if she sees this after her period has ended, then the ruling is that it is taahir (pure), but it requires her to do wudoo’ only. But if she sees it during the time of her period, then it comes under the rulings of menstruation.
And Allaah knows best.