Urwah bin al-Zubayr said: Marwan discussed with me the touching of the penis, and I said: It does not require ablution. Marwan said: Busrah bint Safwan (may Allah be pleased with her) narrates a hadith about it. So he sent a messenger to her, and he reported that she had told him that the Prophet (peace and blessings be upon him) said: "Whoever touches his private part, let him perform ablution."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20870