(14) باب تَغْلِيظِ تَحْرِيمِ الْجِمَاعِ فِي نَهَارِ رَمَضَانَ عَلَى الصَّائِمِ وَوُجُوبِ الْكَفَّارَةِ الْكُبْرَى فِيهِ وبيانها وأنها تجب على الموسر والمعسر وتثبت في ذمة المعسر حتى يستطيع
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 (ﷺ) commanded him to free a slave (as an atonement), and the rest of the hadith is the same as narrated by Ibn Uyaina.
Reference: Sahih Muslim 1111 d
In-book reference: Book 13, Hadith 104
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2460