Sayyidah Busrah bint Safwan al-Asadiyyah (may Allah be pleased with her) said: the Messenger of Allah (peace and blessings be upon him) said: "Whoever touches his private organ, let him perform ablution." Urwah said: I asked Busrah myself, and she confirmed it.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20887