And Ata said that if a fasting person put water in his nose and it went down into his throat, then there is no harm if he cannot expel it. And Imam Hasan al-Basri said that if a fly enters the throat of a fasting person, his fast is not invalidated. And Imam Hasan al-Basri and Mujahid said that if someone has intercourse forgetfully, then making up the fast is not obligatory upon him.

Narrated Abu Huraira: The Prophet said, "If somebody eats or drinks forgetfully then he should complete his fast, for what he has eaten or drunk, has been given to him by Allah."