It is narrated from Sayyidah Umm Habibah (may Allah be pleased with her) that she said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Whoever touches his private part, let him perform ablution (wudu)."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19751