Is it permissible to offer the value of a calf in money instead of slaughtering it, in fulfillment of a vow to slaughter a calf upon the realization of a certain matter?

The vow to sacrifice the calf must be fulfilled if the desired outcome, upon which the vow was contingent, materializes. It is not permissible to substitute it with something else, based on the Prophet's (peace be upon him) saying: "Whoever makes a vow that he can fulfill, let him fulfill it," and his saying: "Whoever vows to obey Allah, let him obey Him."