From Sahih Muslim (Hadith 2597):
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 (ﷺ), whereupon he (the Holy Prophet) said:Can you find a slave (to grant him freedom)? He said: No. He (the 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
Reference: Muslim 2597