Anas ibn Malik · The Book of Ghusl and Tayammum

"The Messenger of Allah (ﷺ) said: 'When any one of you gets up after (sleeping) at night, let him not put his hand into the vessel until he has poured water on it two or three times, for none of you knows where his hand spent the night.'"

"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.'"

"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.