لا نسلم أن التثليث مسنون في الغسل
We do not concede that threefold washing has the claimed status of Sunnah in ghusl.
If the threefold washing of limbs in ablution is used as the basis for extending a ruling to another washing, the opponent asks whether the legal status of repetition is actually established in the proposed original. Performing an action three times does not by itself settle its normative status in every setting.
If that characteristic was not proved with the necessary legal force, the proposed extension fails at its starting point. The relevant inquiry is the act, its setting, and the precise ruling sought.