It is narrated from Sayyidah Busrah bint Safwan (may Allah be pleased with her), or from Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "When one of you touches his penis, let him perform ablution."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20861