Sahih al-Bukhari 6821
Narrated Abu Huraira:
A person had sexual relation with his wife in the month of Ramadan 
     (while he was fasting), and he came to Allah's Messenger (ﷺ) seeking his 
     verdict concerning that action. The Prophet (ﷺ) said (to him), "Can you 
     afford to manumit a slave?" The man said, "No." The Prophet (ﷺ) said, "Can
     you fast for two successive months?" He said, "No." The Prophet (ﷺ) said, 
     "Then feed sixty poor persons."
حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَجُلاً، وَقَعَ بِامْرَأَتِهِ فِي رَمَضَانَ، فَاسْتَفْتَى رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏"‏ هَلْ تَجِدُ رَقَبَةً ‏"‏‏.‏ قَالَ لاَ‏.‏ قَالَ ‏"‏ هَلْ تَسْتَطِيعُ صِيَامَ شَهْرَيْنِ ‏"‏‏.‏ قَالَ لاَ‏.‏ قَالَ ‏"‏ فَأَطْعِمْ سِتِّينَ مِسْكِينًا ‏"‏‏.‏