Question: With respect to blood flowing out, what are the situations in which it nullifies the fast?
Response: The fast is not nullified except by cupping according to that which is correct. There is a strong difference of opinion in this and many see that the fast is not nullified even by cupping. However, the consensus is that cupping nullifies the fast.
Shaykh Ibn Baaz
Fataawa Ramadhaan – Volume 2, Page 476, Fatwa No. 416. fatwaonline.com