I only bled for one day. Is that hayd, and do I still pray?

It depends on your madhab. The Shafi'is and Hanbalis say hayd lasts at least a day and a night, so a few hours of blood is not hayd and you still pray and fast. The Hanafis set the minimum at three days, so even two days of blood is not hayd for them. The Malikis set no minimum at all, so a short bleed counts as hayd. Ibn Taymiyyah also held there is no minimum, and looked at the blood itself and your usual pattern instead.

What the texts say

• The Qur'an calls menstruation "adha", a harm, and ties the ruling to the blood being present and then ending in purity: ﴿وَيَسْأَلُونَكَ عَنِ الْمَحِيضِ قُلْ هُوَ أَذًى فَاعْتَزِلُوا النِّسَاءَ فِي الْمَحِيضِ وَلَا تَقْرَبُوهُنَّ حَتَّىٰ يَطْهُرْنَ﴾ "They ask you about menstruation. Say: it is a harm, so keep away from women during menstruation and do not approach them until they are pure" (al-Baqarah 2:222). The verse gives no number of days, which is why the schools set limits from custom and women's experience.
• Fatimah bint Abi Hubaysh (radi Allahu 'anha) was told by the Prophet (Salla Allahu 'Alayhi Wa Sallam): "When it is menstrual blood it is dark and recognizable, so when it is like that, stop praying, and when it is otherwise, do wudu and pray, for that is from a vein" (narrated by Abu Dawud and al-Nasa'i; classed as sahih by Ibn Hibban and al-Hakim). Blood that does not fit the description of hayd is treated as istihadah, and it does not stop prayer or fasting.

What each school says about a short bleed

• Hanafis: the minimum for hayd is three days. Blood that stops before then is not hayd; it is istihadah (IslamQA.org, Hanafi answer 125876).
• Shafi'is and Hanbalis: the minimum is one day and one night. Bleeding that ends before a full day and night is not hayd, so you pray and fast, with wudu for each prayer (Islamweb, fatwa 12120; Dar al-Ifta Jordan, fatwa 225580).
• Malikis: there is no set minimum, even one gush of menstrual blood counts as hayd. If you follow this school and the blood was menstrual, you treat it as hayd and make ghusl when it ends.
• Ibn Taymiyyah: there is no minimum or maximum; what decides it is whether the blood is menstrual blood and fits your usual pattern.

See what counts as hayd for the full table of minimums and maximums.

What this means for you

1. If the blood was very short, such as a few hours or one day, and you follow the Hanafi, Shafi'i or Hanbali view, you have not had hayd. You pray and fast, and any prayer or fast you left during those hours is still owed. How to count the fasts you owe shows the method.
2. If you follow the Maliki view and the blood was menstrual in colour, thickness and smell, it was hayd. You make ghusl when it ends; see ghusl after hayd.
3. If the blood stops and then returns within a few days, that is a different question; when the bleeding stops and comes back covers it.
4. If the bleeding falls outside your usual days or does not look like your period, it may be istihadah rather than hayd, and the wudu-and-pad routine for prayer applies.
5. To know when your period has really ended, rely on the two signs of tuhr, not only on the calendar.

Because the schools differ, follow the school you normally follow and keep to it. Noting the date, the hours and what the blood looked like helps you or a scholar settle it; a period tracker for Muslim women that logs what you saw, not only a date, makes this easier.

This is a fiqh page, not medical advice. If you often bleed for only a day, or the bleeding is unusually short, light, heavy or painful, or comes between periods, it is worth raising with a doctor.

This page is a study aid compiled from cited classical sources. It is not a fatwa. For your own situation, ask a scholar you trust.