Is frozen blood on wounds considered a barrier that necessitates its removal for ablution, and what is the ruling on prayers performed before the removal of frozen blood that is later found to have been on a wound that had healed?

Slight blood remaining on a wound is usually pardoned, especially if the person is frequently exposed to wounds. The same applies to slight dirt under the fingernail or inside the nose, or any slight substance that prevents water from reaching [the skin], such as blood or dough. This leniency is due to widespread affliction and the hardship of guarding against it. If a servant is afflicted with obsessive thoughts, he must completely disregard them.