What is the ruling on a fasting person breaking their fast due to hunger, and what is the expiation for that?

"Merely feeling hungry is not a permissible excuse for breaking the fast in Ramadan. Whoever breaks their fast for that reason must repent and make up that day. The Malikis have also gone to the extent of obligating expiation (kaffarah), while others have said it is not obligatory, which is the more preponderant opinion. The gravity of the sin of one who breaks their fast without a valid permission is indicated by the Prophet's (peace and blessings be upon him) saying: 'Whoever breaks a day of fasting in Ramadan without a permission, fasting for a lifetime will not compensate for it.'"