Is it necessary to change one's inner and outer garments before every prayer if a part of the urethral opening from inside the penis touches the inner garments?

If the尿道口 (urinary exit) becomes purified in the prescribed manner during istinja (washing after relieving oneself), then its contact with clothes does not cause harm, because it is ruled to be pure, and that which is pure does not become impure by meeting that which is pure. One must beware of waswas (whispers/obsessive thoughts) and not give in to them.