What is the ruling on fasting when one swallows blood with saliva during the Ramadan fast, whether this occurs unintentionally during prayer or outside of it?

It is not permissible to swallow blood, whether one is fasting or not. Swallowing it intentionally invalidates the fast according to the majority of scholars, and this is the correct view. Just as it invalidates the fast, it also invalidates the prayer. However, if the questioner is not certain that he swallowed blood during the prayer, his prayer is not invalidated. He must make up for the day of fasting on which he swallowed blood along with his saliva.