The Messenger of Allah said: "When a man sits between the four parts (arms and legs of his wife) and has intercourse, then bath is obligatory."
Sunan Ibn Majah Book 1, Hadith 344
← Previous Hadith "That was a concession that was granted in the early days of Islam, then we were commanded to have a bathe after that."

Sunan Ibn Majah Book 1, Hadith 343 Next Hadith → "The Messenger of Allah said: 'When the two circumcised parts meet, and (the tip of the penis) disappears, then bath is obligatory.'"

Sunan Ibn Majah Book 1, Hadith 345