John Wesley on Leviticus 27:26

No man shall sanctify it - By vow; because it is not his own, but the Lord's already, and therefore to vow such a thing to God is a tacit derogation from, and an usurpation of the Lord's right, and a mocking of God by pretending to give what we cannot withhold from him. Or ox or sheep - Under these two eminent kinds he comprehends all other beasts which might be sacrificed to God, the firstlings whereof could not be redeemed but were to be sacrificed; whereas the firstlings of men were to be redeemed, and therefore were capable of being vowed, as we see, 1Sam 1:11.