Sahih Muslim
The Book of Fasting (Kitab Al-Sawm)
Book Number: 006 / Hadith Number: 2461
Humaid b. 'Abd al-Rahman reported that Abu Huraira had narrated to him that the Apostle of Allah (may peace be upon him) commanded the person (who) broke the fast in Ramadan to free a slave or observe fasts for two (consecutive) months or feed sixty poor persons.