If someone makes an oath or a vow to themselves, is expiation (kaffarah) obligatory?

The intention to perform an act of obedience or the resolve to do so does not necessitate expiation (kaffarah). One who intends to do good should proceed with it. However, if someone takes an oath that requires expiation and then breaks it, expiation is due. And whoever makes a vow to perform an act of obedience must fulfill it, for the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Allah, let him not disobey Him."