Short answer
Stop praying: the prayer ends as soon as the blood appears. In the Hanafi school, if it was the fard prayer of the current time, you do not make it up, because the period lifts that prayer from you. If it was a sunnah or nafl prayer, you make it up after your period, since a voluntary prayer you begin becomes binding. An old missed prayer you were making up stays owed.
If menstruation begins during the fard prayer of the current time, before its time has ended, the prayer is void and she owes no qada for it. A qada prayer she was making up remains owed. If it begins during a nafl prayer or a nafl fast she had started, she makes it up after becoming pure, because starting a nafl makes completing it wajib. A Ramadan fast is made up in all cases.
Other madhhabs
- Shafi'i
- If enough of the prayer's time had passed before the period for her to have prayed it, she makes up that fard. A voluntary prayer that is cut off is not made up.
- Hanbali
- If the prayer's time had already begun before the period started, she makes up that fard. A voluntary prayer that is cut off is not made up.
Explanation
Bleeding that starts in the middle of salah ends the prayer at once, because being free of menstruation is a condition of every prayer. Leave the prayer, see to yourself, and do not worry about finishing it.
Do you make it up? The Hanafi school holds that the obligation of a prayer settles on the last part of its time. If your period starts anywhere inside the time, before you have finished praying, the prayer of that time is lifted from you, whether you had started it or not. So a fard prayer cut off by the period is not made up. This is the same rule as a period that starts in a prayer's time before you prayed it. See making up prayers missed during a period.
Voluntary prayers are different. In the Hanafi school a voluntary prayer or fast becomes binding once you start it, because Allah says: do not invalidate your deeds. So if your period cuts off a sunnah or nafl prayer, such as the sunnah of Zuhr or tahajjud, you pray those two rakats later after ghusl. If it cuts off a voluntary fast, such as a Monday or the day of Arafah, you fast a day in its place.
Quick guide:
- Fard prayer of the current time cut off by the period: no make-up.
- An old qada prayer cut off: still owed; pray it after your period.
- Sunnah or nafl prayer cut off: pray it later.
- Ramadan fast cut off: make up the day. See period during a Ramadan fast.
- Voluntary fast cut off: make up one day.
If you are praying with others, a quiet exit is enough, and no one needs to be told why.
The evidence
Quran, Surah Al-Baqara 2:222
وَيَسْـَٔلُونَكَ عَنِ ٱلْمَحِيضِ ۖ قُلْ هُوَ أَذًۭى فَٱعْتَزِلُوا۟ ٱلنِّسَآءَ فِى ٱلْمَحِيضِ ۖ وَلَا تَقْرَبُوهُنَّ حَتَّىٰ يَطْهُرْنَ ۖ فَإِذَا تَطَهَّرْنَ فَأْتُوهُنَّ مِنْ حَيْثُ أَمَرَكُمُ ٱللَّهُ ۚ إِنَّ ٱللَّهَ يُحِبُّ ٱلتَّوَّٰبِينَ وَيُحِبُّ ٱلْمُتَطَهِّرِينَ ﴿٢٢٢﴾
And they ask you about menstruation. Say, "It is harm, so keep away from wives during menstruation. And do not approach them until they are pure. And when they have purified themselves, then come to them from where Allah has ordained for you. Indeed, Allah loves those who are constantly repentant and loves those who purify themselves."
Menstruation has its own rulings for prayer.
Quran, Surah Muhammad 47:33
۞ يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ أَطِيعُوا۟ ٱللَّهَ وَأَطِيعُوا۟ ٱلرَّسُولَ وَلَا تُبْطِلُوٓا۟ أَعْمَٰلَكُمْ ﴿٣٣﴾
O you who have believed, obey Allah and obey the Messenger and do not invalidate your deeds.
The Hanafi proof that a voluntary act once started must be completed or made up.
Sahih al-Bukhari 304
Sahih... أليس إذا حاضت لم تصل ولم تصم ...
"Is it not so that when she menstruates she neither prays nor fasts?"
Prayer is lifted from a woman during her period.
Where the ruling is recorded
- al-Durr al-Mukhtar, Kitab al-Taharah, chapter on haid. If her period comes during a fard prayer it is lifted; during a voluntary prayer she makes it up.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Taharah, chapter on haid. Explains that the obligation rests on the last part of the time.
- al-Majmu' (Nawawi), Kitab al-Salah, the times of prayer, women whose period starts in the time. Makes up the fard if enough time had passed to pray it.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.