It was narrated that Ibn 'Umar said:

"Umar mentioned to the Messenger of Allah ﷺ that he became Junub at night, and the Messenger of Allah ﷺ said: 'Perform Wudu' and wash you penis, then sleep.'"

أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ ذَكَرَ عُمَرُ لِرَسُولِ اللَّهِ ﷺ أَنَّهُ تُصِيبُهُ الْجَنَابَةُ مِنَ اللَّيْلِ فَقَالَ رَسُولُ اللَّهِ ﷺ " تَوَضَّأْ وَاغْسِلْ ذَكَرَكَ ثُمَّ نَمْ " .