What is the ruling on someone who masturbates and semen or prostatic fluid splashes onto his bed, his siblings' beds, or their belongings – are they sinful if they do not wash it and pray?

We advise you to repent to Allah from masturbation because it is forbidden, and to turn away from obsessive thoughts and ignore them. Semen, according to the preponderant opinion of scholars, is pure, so it does not defile the bedding it gets on, nor is it obligatory to wash it.