Busrah bint Safwan (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever touches his private part, let him perform ablution." Urwah said: I asked Busrah (may Allah be pleased with her), and she confirmed it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 621