What are the things that are excused if found on a worshiper's garment?

Avoiding impurities on one's garment, body, and place of prayer is a condition for the validity of prayer according to the majority of scholars. The evidence for this condition regarding garments is Allah's saying: "And purify your garments." A small amount of impurity that is difficult to avoid is pardoned, such as a small amount of blood or pus. As for what is not impure, like mucus and semen, it is not obligatory to avoid them, but it is preferable to keep one's garment free from them. Scholars differ on the amount of impurity that is pardoned: the Hanafis pardon an amount of severe impurity equivalent to a dirham; the Malikis made concessions regarding avoiding impurities when there is difficulty; and the Shafi'is stated that a small amount of blood and pus is pardoned. As for the Hanbalis, they do not pardon a small amount of impurity except for a small amount of blood and what originates from it. Sheikh al-Islam Ibn Taymiyyah chose to pardon all small amounts of impurities. Avoiding impurities is conditioned upon knowledge and ability; thus, whoever is unable to remove it, or forgets it, or is unaware of it, their prayer is valid. If one finds no garment except an impure one, the preponderant opinion with us is that they should pray naked, and no repetition is required of them.