What is the ruling on one who breaks their fast by mistake in Ramadan, and does this entail the same consequences as breaking the fast out of forgetfulness?

The Sharia indicates the removal of blame from one who forgets or makes a mistake. Forgetfulness is an excuse for committing prohibitions, but not for neglecting commands. The removal of sin does not mean the annulment of liability.

Firstly: Whoever eats or drinks forgetfully does not break their fast, according to the majority of scholars. However, Malik holds that making up the fast is obligatory during Ramadan, but not at other times.

Secondly: Regarding one who engages in intercourse forgetfully, jurists differ. The Hanafis and Shafi’is hold that it does not invalidate the fast, while the Malikis deem making it up obligatory. The Hanbalis obligate making it up and expiation. Ibn Taymiyyah chose against both making it up and expiation.

Thirdly: Whoever eats or drinks by mistake (believing it is still night or that the sun has set) must make up the fast without expiation, according to the majority of scholars. Ibn Taymiyyah, however, believes that making up the fast is not obligatory. If the mistake is not clear, there is no need to make up the fast, according to the Hanbalis and Hanafis.

Fourthly: If one engages in intercourse believing it to be night, and it turns out to be day, they must make up the fast without expiation, according to the majority of scholars. The Hanbalis obligate both making up the fast and expiation. Ibn Taymiyyah chose against both making up the fast and expiation.

Forgetfulness is not an excuse in all scenarios, and mistake differs from forgetfulness in some matters.