The Messenger of Allah (May peace be upon him) said : water (bath) is necessary only when there is seminal emission. And Abu Salamah followed it.
Sunan Abi Dawud Book 1, Hadith 217
← Previous Hadith when anyone sits between the four parts of a woman and the parts (of the male and female) which are circumscised join together, then bath becomes obligatory.

Sunan Abi Dawud Book 1, Hadith 216 Next Hadith → One day the Messenger of Allah (May peace be upon him) had sexual intercourse with (all) his wives with a single bath.

Abu Dawud said: This tradition has been transmitted through another chain of narrators.

Sunan Abi Dawud Book 1, Hadith 218