Sahih Bukhari Volume 9, Book 83, Hadith Number 25.

Narrated By ‘Aisha : We poured medicine into the mouth of the Prophet during his ailment. He said, “Don’t pour medicine into my mouth.” (We thought he said that) out of the aversion a patient usually has for medicines. When he improved and felt better he said, “There is none of you but will be forced to drink medicine, except Al-‘Abbas, for he did not witness your deed.”