It was narrated from Abu Hurairah that:
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." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 610 (RU)
Arabic reference (RU): Book 1, Hadith 653 (RU)