Urwah said: I was with Marwan bin al-Hakam when I was asked about touching the private organ, and I did not consider it necessary to repeat the ablution for it. So Marwan called one of his guards and sent him to Busrah bint Safwan (may Allah be pleased with her). He asked her about that, and she told him that the Messenger of Allah (peace and blessings be upon him) said: "When one of you touches his private organ, let him repeat the ablution."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20882