What must be done upon doubting or ascertaining that urine has exited; should only the underwear be changed or all clothes?

Among the known principles is that the default is for certain things to remain as they are, and one does not deviate from them merely due to doubts. The proof for this is the Prophet's (peace be upon him) saying: "He should not leave until he hears a sound or perceives a smell." Based on this principle, whoever doubts the emission of urine is not required to wash his clothes or body until he is certain that urine has been emitted and has come into contact with them. However, if the urine is due to incontinence (sals), it has a different ruling.