What is the clarification of the statement that passing gas does not necessitate washing the front and back private parts, and in fact, it is not legislated?

It is not obligatory to perform istinjāʾ (cleansing after defecation or urination) for passing wind, nor is it legislated at all. Indeed, whoever does so believing it to be legislated has committed an innovation (bidʿah). Istinjāʾ is performed for urine, feces, madhy (pre-seminal fluid), wady (thick white discharge after urination), or similar substances that exit from the two private parts and leave a trace on the area. Whoever invalidates their ablution (wuḍūʾ) by passing wind is only required to perform ablution.