"Busrah bint Safwan told me that." 'Urwah sent someone to check that, and she said: "The Messenger of Allah (ﷺ) mentioned what Wudu' is done for, and said: 'Touching the penis.'"
Sunan an-Nasa'i Book 4, Hadith 52
← Previous Hadith "If any one of you touches his private part with his hand, let him perform Wudu'."

Sunan an-Nasa'i Book 4, Hadith 51 Next Hadith → "Whoever touches his penis, he should not perform Salah until he performs Wudu'." Abu 'Abdur-Rahman (An-Nasa'i) said: Hisham bin 'Urwah did not hear this Hadith from his father.

Sunan an-Nasa'i Book 4, Hadith 53