Is it obligatory to repeat the ritual bath (ghusl) and the prayer (salat) after seeing drops of blood on the underwear following a ghusl from janabah (major ritual impurity), knowing that the private parts were washed before rinsing the mouth and nose?

The emission of blood from the body does not necessitate ghusl (ritual bath) except for menstrual and post-natal bleeding. Similarly, its emission from non-private parts (the two passages) does not invalidate wudu (ablution). However, if blood exits from one of the two private parts, it invalidates wudu. If the time of its emission is unknown, it is attributed to the nearest possible time. So, if one sees it after performing wudu and before prayer, they must repeat both wudu and prayer if they have already prayed. But if they see it after performing wudu and prayer, they are not obligated to repeat the prayer, because the original assumption is that it was validly performed.