Reference: Fataawa Ramadhaan – Volume 2, Page 460, Fatwa No.393
Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-`Ilmiyyah wal-Iftaa. – Fatwa No.12077
Question: During Ramadhaan, while I was fasting I had a nosebleed and the blood entered my body (i.e. flowed down the back of my throat and into the stomach).
Response: Blood flow from a nosebleed does not break the fast, since it was not caused intentionally. However, if you were to intentionally swallow the blood, then you are required to make up the fast for this day. That is, if you had swallowed it after it reached your mouth, remembering that you were fasting.
And with Allaah lies all the success, and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.