Sahih Muslim Book 6, Hadith Number 2459.

Chapter : Sexual Intercourse is completely forbidden during the day in the month of Ramadhan.

Abu Huraira reported that a person had intercourse with his wife during Ramadan (while fasting). He asked for the religious verdict (about it) from the Messenger of Allah (may peace be upon him), whereupon he (the Holy Prophet) said: Can you find a slave (to grant him freedom)? He said: No. He (the Holy Prophet again) said: Can you afford to observe fasts for two (consecutive) months? He said: No. He (the Holy Prophet) said: Then feed sixty poor men.