Mishkat al-Masabih 3 Purification كتاب الطهارة 156

وَعَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ أَنه قَالَ: ذَكَرَ عُمَرُ بْنُ الْخَطَّابِ لِرَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ تُصِيبُهُ الْجَنَابَةُ مِنَ اللَّيْلِ فَقَالَ لَهُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «تَوَضَّأْ وَاغْسِلْ ذَكَرَكَ ثُمَّ نم»

Ibn ‘Umar told how ‘Umar b. al-Khattab mentioned to God’s messenger that he was affected by seminal defilement during the night, and was told to perform ablution, wash his penis, and go back to sleep. (Bukhari and Muslim.)