Wudu and bleeding gums
The general principle is that if blood flows from a part of the body then the ablution is nullified. If blood appears on the surface but does not flow beyond the point of exiting, it does not nullify ablution.
The mouth is naturally wet. It is therefore not easy to tell whether blood actually flowed out from the gums or was just on the surface and was carried out by the saliva in which case the ablution would not be nullified. That is why the colour of the saliva is considered in such a case.
Imam al-Haskafi says in al-Durr al-Mukhtar,
“And it [the ablution] is nullified by blood…that predominates over the saliva or equals it. It is not nullified if the saliva predominates.”
Ibn Abidin explains that,
“The sign of the blood being predominate or equal is that the saliva is red and the sign of the saliva being predominate is that saliva is yellow.” [Radd al-Muhtar `ala al-Durr al-Mukhtar, ‘Bab al-Wudu’]
Likewise, if one spits out clear saliva with a thin streak of blood it can be assumed that the blood did not flow and so the ablution is not nullified, though a larger quantity of blood could indicate the contrary. One should use one’s reasonable judgment.
If unable to spit out, one should rely on past experience or common sense to determine whether such blood would have predominated over the saliva or not. The default is that it would not have, and that one’s wudu remains valid
It has been explained in previous posts that certainty is not lifted by mere doubt. If one has certainty that one has performed ritual ablutions and merely doubts whether one’s gums have bled excessively, as described above, then one will adhere to the certainty, namely that one is still in a state of ritual purity.
[Umm Umar notes: gum bleeding normally is a result of poor dental hygiene, and one should brush properly twice a day and floss daily.]
And Allah knows best.
Sohail Hanif , with Faraz Rabbani