Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.138B.

If one is overcome and vomits unintentionally, he does not have to make up the day later on or perform the acts of expiation. Abu Hurairah reported that the Prophet, upon whom be peace, said: “Whoever is overcome and vomits is not to make up the day.” Whoever vomits intentionally must make up the day.” This is related by Ahmad, Abu Dawud, at-Tirmizhi, Ibn Majah, Ibn Hibban, ad-Daraqutni, and al-Hakim. The latter called it sahih.

Of the report’s credibility, al-Khattabi says: “I do not know of any difference of opinion among the scholars on this point. If one vomits unintentionally he is not in need of making up the day, while one who vomits intentionally must make up the day later.”