Shaykh bin Baz (rahimahullah) was asked:

One day I was making up an obligatory fast and after Dhuhr I felt hungry, so I ate and I drank intentionally and not out of forgetfulness, what is the ruling on this?

Obligatory upon you is to complete the fast, it is not permissible to break the fast if the fast was an obligatory one, such as making up a fast from Ramadhaan or a fast which you vowed to perform, upon you is to repent from what you have done and whoever repents (sincerely), Allah accepts their repentance.

Paraphrased from Majmoo’ Fataawa Shaykh bin Baz (rahimahullah) Vol.15 page 355