How much vomit invalidates the fast?
General Chapter
Al-Mughni
Book of Fasting
Primary text
The apparent view, one narration from Ahmad, and the position taken by the ruling scholar is that any quantity of vomit, whether little or much, invalidates the fast. This is based on the apparent meaning of the hadith concerning vomiting, and because other nullifiers of the fast do not differentiate between small and large quantities.
Supporting text
A second narration from Ahmad states that the fast is only invalidated if the vomit fills the mouth, citing the hadith: 'But a quantity that fills the mouth.' A third view states that half a mouth-full invalidates it, reasoning that since it invalidates ablution, it invalidates the fast, similar to a large amount.