Do Bleeding Gums Break Fast?
Question

Does the blood that comes out from between the teeth accidentally invalidate the fast or not? What if it is caused by the person himself, rather it is caused by another person hitting him by mistake? Please advise us, may Allah reward you.
Praise be to Allah.“The blood that comes out from between the teeth does not invalidate the fast, whether it comes out by itself or because of another person hitting him. 
And Allah is the source of strength. May Allah send blessings and peace upon our Prophet Muhammad and upon his family and Companions.” (Al-Lajnah al-Daimah li’l-Buhuth al-‘Ilmiyyah wa’l-Ifta, 10/267) 
But it is haram for the fasting person to swallow this blood ; if he swallows it deliberately then his fast is broken.
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And Allah knows best.