Is a vow to sacrifice fulfilled by slaughtering the father's seated ram instead of the promised calf?

If the one who made the vow did not specify a particular calf, he may slaughter one that is equal to or greater than it in price. If the substitute is better than what was vowed, is it all obligatory or only part of it? There are two opinions: one is that one-seventh of it is obligatory and the rest is voluntary; the second is that all of it is obligatory.

If the one who made the vow did not specify the vow and did not designate its age and description, then the Maliki and Shafi'i schools of thought oblige the minimum that the Law has enjoined of that type, and they stipulate the age that is sufficient for sacrifice and freedom from defects.

However, if the one who made the vow specified what he vowed, whether it was small or large, he is bound by what he specified, and it is not permissible to substitute it.

When fulfilling the vow, it is required to have the intention that what is slaughtered is in fulfillment of the vow. There is no harm if the one who made the vow appoints someone else to slaughter on his behalf.