Sahih Muslim Book 3, Hadith Number 606.

Chapter : It is permissible for a person to sleep after sexual intercourse (without a bath) and the desirability of ablution for him, and washing of the sexual organ, as he intends to eat, drink, or sleep or cohabit.

Anas reported: The Messenger of Allah (may peace be upon him) used to have sexual intercourse with his wives with a single bath.