Is it permissible to pray in clothes stained with blood from an internal hemorrhage, given the inability to change them at work?

The worshipper must purify his garment from impurity, based on the Almighty's saying: (And purify your garments), otherwise, he must change them before prayer.

The spread of blood can be minimized by using a cloth or tissue and changing it when performing ablution and washing the bloodied area.

If that is difficult, then there is no harm in praying with those clothes.

Sheikh Ibn Baz said: "A sick person afflicted with urinary incontinence who has not recovered despite treatment must perform ablution for every prayer after its time has begun, wash whatever affects his body, and wear a pure garment for prayer if that is not difficult for him. Otherwise, he is excused, based on Allah the Almighty's saying: (And He has not placed upon you in religion any difficulty), and His saying: (Allah intends for you ease and does not intend for you hardship), and the Prophet's (peace be upon him) saying: (When I command you to do something, do of it as much as you are able). And he should take precautions to prevent the spread of urine on his clothes, body, or prayer area."