There is an agreement among Muslim scholars that bleeding from the two natural orifices breaks wudu’. Bleeding from a cut or wound, however, does not break wudu’.
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “Bleeding from any of the natural orifices (anus, urethra or vagina) definitely breaks one’s wudu’. This is the general consensus among the scholars.
Bleeding from a cut or wound, however, does not break one’s wudu’. This is supported by strong evidence in the primary sources of Islam and is endorsed by the Salaf (the pious predecessors). It is common knowledge that the Companions used to pray while they were bleeding from their wounds. Caliph `Umar (may Allah be pleased with him) prayed while bleeding from stab wounds. The above rule also applies to blood taken for medical tests.”