Muhammad bin 'Abdullah bin Muslim محمد بن عبد الله بن مسلم · The Book of Ghusl and Tayammum

"Ali bin Abi Talib sent Al-Miqdad to the Messenger of Allah (ﷺ) to ask him about a man who notices Madhi. The Messenger of Allah (ﷺ) said: 'Let him wash his penis then perform Wudu'.'"