If someone is overcome by vomiting during the day of Ramadan, meaning vomiting that is not caused by him, then it is considered: if the vomit fills the mouth, and if the vomit returns by itself, then it does not invalidate his fast, which is the correct opinion. If the vomit fills the mouth, it is because he did not exhibit the act of breaking the fast, which is swallowing, and its meaning is the same; since he does not gain nourishment from it. If he brings up the vomit by his own action or if he brings up a portion the size of a chickpea or more, then it invalidates his fast, and he must make up for it, as long as its origin is filling the mouth. If the vomit comes out and he does not bring it back nor does it return by itself, then it does not break his fast. As for if the vomit is less than filling the mouth: if the vomit returns by itself, then it does not invalidate his fast. If he brings up the vomit by his own action, then it does not invalidate his fast, which is the correct opinion; due to the lack of expulsion; since filling the mouth has the ruling of expulsion, and anything less than that is not considered expelled; because it can be controlled. If the vomit comes out and he does not bring it back nor does it return by itself, then it does not break his fast. Refer to Tabyin 1: 325-326, and Radd al-Muhtar 2: 111.