Short answer
In the Hanafi school, the prayer is valid if the impurity is no larger than a dirham, roughly the hollow of your palm, but praying with that amount knowingly is makruh tahrimi, so wash it if you can. More than a dirham makes the prayer invalid. The Shafi'i school excuses only tiny amounts.
Urine, stool, flowing blood and similar heavy impurity (najasah ghalizah) on clothes, body or the place of prayer is excused up to the area of a dirham. Praying knowingly with a dirham's worth is makruh tahrimi; more makes the prayer invalid. Blood that does not flow, such as a pinprick spot, is not impure.
Other madhhabs
- Shafi'i
- Impurity is excused only when it is too small to see, except small amounts of blood and pus, which are excused.
- Maliki
- Removing impurity is required when you remember it and are able to. A little blood, less than a dirham, is excused.
- Hanbali
- A small amount of blood and pus is excused; urine and stool are not excused in any amount.
Explanation
Purity of body, clothes and place is a condition of prayer. Allah tells the Prophet ﷺ to purify his clothing, and he warned that one of two men punished in the grave did not guard himself from his urine.
The Hanafi school sets a practical limit, the dirham. For a liquid, that is an area about the size of the hollow of the palm. For a solid, it is a dirham's weight.
- Up to a dirham: the prayer is valid, but wash it first if you can.
- More than a dirham: the prayer is not valid until you wash it or change.
- Tiny splashes of urine like pinpoints: excused, because no one can avoid them.
Blood: only flowing blood is impure, which the Quran calls "blood spilled out". A spot from a pimple or pinprick that did not flow is not impure. Blood of fish and of mosquitoes and fleas is not impure either. To wash menstrual or other blood from cloth, the Prophet ﷺ described scraping it, rubbing it with water, rinsing it and then praying in it. A remaining stain that will not come out after washing is excused.
How to wash: for visible impurity, wash until it is gone. For invisible impurity like dried urine, wash and squeeze three times. If you find impurity after praying, see doubts about purity, and ask a mufti if it was more than a dirham.
The evidence
Quran, Surah Al-Muddaththir 74:4
وَثِيَابَكَ فَطَهِّرْ ﴿٤﴾
And your clothing purify
The command to keep clothes pure.
Quran, Surah Al-An'aam 6:145
قُل لَّآ أَجِدُ فِى مَآ أُوحِىَ إِلَىَّ مُحَرَّمًا عَلَىٰ طَاعِمٍۢ يَطْعَمُهُۥٓ إِلَّآ أَن يَكُونَ مَيْتَةً أَوْ دَمًۭا مَّسْفُوحًا أَوْ لَحْمَ خِنزِيرٍۢ فَإِنَّهُۥ رِجْسٌ أَوْ فِسْقًا أُهِلَّ لِغَيْرِ ٱللَّهِ بِهِۦ ۚ فَمَنِ ٱضْطُرَّ غَيْرَ بَاغٍۢ وَلَا عَادٍۢ فَإِنَّ رَبَّكَ غَفُورٌۭ رَّحِيمٌۭ ﴿١٤٥﴾
Say, "I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine - for indeed, it is impure - or it be [that slaughtered in] disobedience, dedicated to other than Allah. But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], then indeed, your Lord is Forgiving and Merciful."
Flowing blood is what is impure, not every trace of blood.
Sahih al-Bukhari 216
Sahih... وكان الاخر لا يستتر من بوله ...
"And the other did not guard himself from his urine."
Carelessness with urine is a sin punished in the grave.
Sahih al-Bukhari 227
Sahih... تحته ثم تقرصه بالماء وتنضحه وتصلي فيه ...
"She scrapes it, rubs it with water, rinses it, and then prays in it."
How to wash blood from clothes and pray in them.
Where the ruling is recorded
- al-Hidaya, Kitab al-Taharat, chapter on impurities and their purification. Heavy impurity is excused up to a dirham.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Taharah, chapter on impurities. The dirham by area and by weight; praying with it is makruh tahrimi.
- al-Majmu' (Nawawi), Kitab al-Taharah, chapter on removing impurity. The Shafi'i rule on excused amounts.
This answer is pending review by the scholars on our team. 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.