Will my prayer be accepted if I find a spot of blood or seminal fluid on my clothes after I have finished it, and must I repeat it?

The prayer is valid if there was impurity on the clothes after the prayer without the worshiper's knowledge, bearing in mind that a small amount of blood is excused.

As for the fluid, if it is semen, it is pure according to the preponderant opinion, but it necessitates ghusl (ritual bath). If it is found, ghusl becomes obligatory, and previous prayers must be repeated.

However, if it is madhy (pre-seminal fluid), it is impure and invalidates ablution. It must be purified from, and prayers performed without purification must be repeated, as the Prophet, peace and blessings be upon him, said: "Allah does not accept a prayer without purification."