1) Intentionally eating or drinking:
Abu Hurairah narrated that the Prophet said, “Whoever forgets while he is fasting and eats or drinks something should complete his fast, for it was Allah who fed him or gave him to drink.”
2) Sexual intercourse:
Narrated by Abu Hurairah: While we were sitting with the Prophet صلى الله عليه و سلم a man came and said, “O Allah’s Apostle! I have been ruined.” Allah’s Apostle asked what the matter with him was. He replied, “I had sexual intercourse with my wife while I was fasting.” Allah’s Apostle asked him, “Can you afford to manumit a slave?” He replied in the negative. Allah’s Apostle asked him, “Can you fast for two successive months?” He replied in the negative. The Prophet asked him, “Can you afford to feed sixty poor persons?” He replied in the negative. The Prophet kept silent and while we were in that state, a big basket full of dates was brought to the Prophet. He asked, “Where is the questioner?” He replied, “I (am here).” The Prophet said (to him), “Take this (basket of dates) and give it in charity.” The man said, “Should I give it to a person poorer than I? By Allah; there is no family between its (i.e. Medina’s) two mountains who are poorer than I.” The Prophet smiled till his pre-molar teeth became visible and then said, ‘Feed your family with it.’”
4) Al-Haid [menstruation] and An-Nifas [post natal bleeding]:
Aishah said, “We used to menstruate during the time of the Messenger of Allah () and we were ordered to make up the fasts and we were not ordered to make up the prayers.”
Even if these (Menstruation and post-partum) occur at the last moment before sunset, they must break the fast according to the Ijma of the scholars.
 Recorded by Muslim, Bukhari ibn Majah and Tirmizi. This is the wording of Sahih Muslim.
 Recorded by Bukhari