It is narrated from Sayyiduna Abu Darda’ (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) vomited deliberately and then broke his fast. Ma’dan said: I met Sayyiduna Thawban (may Allah be pleased with him) in the mosque of Damascus and mentioned this to him, so Sayyiduna Thawban (may Allah be pleased with him) said: Sayyiduna Abu Darda’ (may Allah be pleased with him) has spoken the truth; I poured water for the Prophet (peace and blessings be upon him).
From this hadith, it is understood that if someone deliberately induces vomiting for any reason, the fast is broken, and according to most scholars, making up (qada) that fast becomes obligatory upon him, but expiation (kaffarah) is not required, whether the vomit is little or much. And if vomiting occurs involuntarily, then the fast is not broken; this is the opinion of the four Imams (a’immah arba‘ah), and in this case, neither making up (qada) nor expiation (kaffarah) is required.