All praise is for Allaah alone and may the salaat and the salaam be upon His Messenger and his family and his Companions…
To proceed: We do not know of a sharee’ah proof to prove that the emergence of blood from other than the private parts is from the nawaaqid ul wudhoo (the nullifiers of the wudhoo) – and the asl (basic principle) is that it is not a nullifier.
And the actions of worship – their basis is upon at-tawqeef (being restricted to a proof from the Book or the Sunnah). So it is not permissible for anyone to say this act of worship is Islaamically legislated except with a proof.
And indeed some of the people of knowledge were firmly upon the opinion that the emergence of a large amount of blood from other than the private parts is from that which nullifies the wudhoo.
So if the person from whom this (blood) comes out makes wudhoo due to being cautious and due to avoiding matters of disagreement then this is hasan (something good) - according to the statement of the Prophet (sal Allaahu alaiyhi wa sallam):
Leave that which causes you doubt for that which does not cause you doubt. (An Nasaa’ee and At Tirmidhee)
And with Allaah is the tawfeeq. And may peace and blessings be upon our Prophet Muhammad and his family and his Companions.