What is the ruling on retracting a vow or promise that cannot be fulfilled?

One must fulfill the vow (nazr) by which one seeks nearness to Allah, as Allah the Almighty says: "They fulfill [their] vows and fear a Day whose evil will be widespread" (Al-Insan: 7), and His saying: "and let them fulfill their vows" (Al-Hajj: 29). And based on the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Him, let him not disobey Him." It is not permissible to retract a vow after it has been made. Whoever is unable to fulfill a vow due to an inability that is not expected to cease must offer an expiation for an oath (kaffarat yameen).