It is narrated from Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever touches his private part, let him perform ablution (wudu)."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5202
Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever touches his private part, let him perform ablution (wudu)."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5203