He got blood on his underwear and it is hard for him to change it
Question

                I have internal bleeding, i.e., blood comes out with the faeces or sometimes it comes out spontaneously on my underwear. I may spend more than 12 hours at work. Can I pray when there is this blood on my underwear or not? Please note that I am at work and cannot change my underwear.
Praise be to Allah.What 
    everyone who wants to pray must do is to purify his clothes of any impurity 
    that is on them, because Allaah says (interpretation of the meaning): 
“And 
    purify your garments”

    [al-Muddaththir 74:4]
And when the 
    Prophet  (peace and blessings of Allaah be upon him) was asked about 
    praying in a garment in which a woman had menstruated, he ordered that it be 
    cleansed of impurity before praying in it. Narrated by al-Bukhaari (308) and 
    Muslim (361). So you have to purify your garment or change it before 
    praying. You can ward off hardship by putting a pad or piece of cloth to 
    stop the blood spreading, then when you do wudoo’ you can change this pad or 
    cloth and wash the part of your body that the blood has gotten on to. If 
    that is also too hard for you, then there is nothing wrong with your praying 
    in this garment. 
Shaykh Ibn 
    Baaz (may Allaah have mercy on him) said: The sick person who is affected 
    with urinary incontinence and does not recover with treatment can do wudoo’ 
    for each prayer after the time for it has begun, and wash off whatever has 
    gotten onto his body, and set aside clean clothes for praying if that is not 
    too difficult for him, otherwise he is forgiven, because Allaah says 
    (interpretation of the meaning): 
“and 
    [Allaah] has not laid upon you in religion any hardship”
[al-Hajj 
    22:78]
“Allaah 
    intends for you ease, and He does not want to make things difficult for you”

    [al-Baqarah 2:185]
And the 
    Prophet  (peace and blessings of Allaah be upon him) said: “If I command 
    you to do a thing, then do as much of it as you can.”  
But he 
    should take precautions to prevent the urine spreading on his clothes or 
    body or the place where he is praying. 
End quote from Fataawa Islamiyyah (1/192) 
And Allaah knows best.