Sahih Muslim Book 6, Hadith Number 2460.
Chapter : Sexual Intercourse is completely forbidden during the day in the month of Ramadhan.
This Hadith has been narrated on the authority of Zuhri with the same chain of transmitters that a person broke fast in Ramadan whereupon the Messenger of Allah (may peace be upon him) commanded him to free a slave (as an atonement), and the rest of the Hadith is the same as narrated by Ibn Uyaina.