Marwan said: Whoever touches his private parts, let him perform ablution. Urwah objected to this, so Marwan said: O guard, go to Busrah bint Safwan and ask her, for she had stated that she heard the Prophet (peace and blessings be upon him) say: "Whoever touches his private organ, let him perform ablution."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20879