Whenever the Prophet (ﷺ) intended to sleep while he was Junub, he used to wash his private parts and perform ablution like that for the prayer.

`Umar asked the Prophet (ﷺ) "Can anyone of us sleep while he is Junub?" He replied, "Yes, if he performs ablution."

`Umar bin Al-Khattab told Allah's Messenger (ﷺ), "I became Junub at night." Allah's Messenger (ﷺ) replied, "Perform ablution after washing your private parts and then sleep."

as the following Hadith 290.

Narrated Abu Huraira:

The Prophet (ﷺ) said, "When a man sits in between the four parts of a woman and did the sexual intercourse with her, bath becomes compulsory."

I asked `Uthman bin `Affan about a man who engaged in the sexual intercourse with his wife but did not discharge. `Uthman replied, "He should perform ablution like that for the prayer after washing his private parts." `Uthman added, "I heard that from Allah's Messenger (ﷺ)." I asked `Ali bin Abi Talib, Az- Zubair bin Al-`Awwam, Talha bin 'Ubaidullah and Ubai bin Ka`b and they gave the same reply. (Abu Aiyub said that he had heard that from Allah's Messenger (ﷺ) ) (This order was canceled later on so one has to take a bath. See, Hadith No. 180).

I asked Allah's Messenger (ﷺ) about a man who engages in sexual intercourse with his wife but does not discharge. He replied, "He should wash the parts which comes in contact with the private parts of the woman, perform ablution and then pray." (Abu `Abdullah said, "Taking a bath is safer and is the last order.")