What is the ruling on abandoning a fast after vowing it to Allah due to an inability to exert effort?

Whoever makes a covenant with Allah to perform an act of obedience and verbally commits to it, it becomes a vow that must be fulfilled. However, if it was merely an internal thought without utterance, then nothing is binding. Allah Almighty has condemned the hypocrites who broke their covenant, saying: "And among them are those who made a covenant with Allah, [saying], 'If He gives us from His bounty, we will surely spend in charity, and we will surely be among the righteous.' But when He gave them from His bounty, they were stingy with it and turned away while they were refusing. So He put hypocrisy in their hearts until the Day they will meet Him, because they broke their promise to Allah and because they used to lie." Therefore, whoever makes a covenant with Allah to fast must fulfill it; if they are unable, they must offer an expiation for breaking an oath.