It is narrated from Sayyidah Busrah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever touches his private part, let him perform ablution and then pray." The narrator said: I came to Sayyidah Busrah (may Allah be pleased with her), and she narrated the hadith to me just as Marwan had narrated it: that she heard the Messenger of Allah (peace and blessings be upon him) saying it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 622