Is it obligatory to perform istinja (washing the private parts) and change underwear upon the emission of irregular discharge from the anus due to hemorrhoids before every prayer? Is it necessary to change outer garments if they are soiled by the discharge? And what should a traveler do in this situation?

If an impurity is discharged, a tissue can be placed on the spot and then removed, and istinja' (ritual cleansing) performed when one intends to pray and perform ablution for it. If you do not do that, the impurity must be removed from the garment by washing the affected area. If its removal is difficult and you are compelled to pray with an impure garment, your prayer is valid. The Malikis are lenient regarding impurity if it is discharged once daily, and they do not obligate its removal.