Is it obligatory to change and wash clothes if they have been stained with blood or yellow fluid resulting from youth pimples, before prayer?

According to the preponderant opinion, blood that exits from other than the two private parts (the anus and the urethra) does not invalidate ablution. This is the view of Malik and Al-Shafi'i, and it was chosen by Ibn Taymiyyah. As for blood or pus that gets on clothes, if it is a small amount, there is no harm; but if it is a large amount, it is obligatory to wash or change the clothes, according to the majority of scholars. Some scholars, like Ibn 'Uthaymeen, held the view that blood exiting from a human body from other than the two private parts is pure (tahir) and not impure (najis).