What is the ruling on one who vowed to slaughter an animal every year in Ramadan and on the Prophet's birthday for the soul of his father, saying, "As long as I am alive and provided for and God makes things easy for me," but is now unable to fulfill this vow?

Whoever vows 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." Charity is an act of proximity [to Allah] and its vow must be fulfilled. If you are unable to fulfill your vow, then the expiation for an oath is required, based on his, peace and blessings be upon him, saying: "The expiation for a vow is the expiation for an oath." This consists of feeding ten poor persons, or clothing them, or freeing a slave. If you are unable to do that, then fasting for three days. Celebrating the Prophet's birthday (Mawlid) is not legislated [in Islam]. If the vow to slaughter on the Mawlid is made with the belief that it brings one closer to Allah and increases rewards, then it is not permissible to fulfill this part of the vow in this manner.