Ibn Ezra on Leviticus 27:26

יבכר לה׳‎. נודע שהוא לשם וזאת המלה מהבנין שלא נקרא שם פועלו ופירושו האומר אתן הבכור לשם: WHICH IS BORN AS A FIRSTLING TO THE LORD. Known to be the Lord’s. Yevukkar (which is born as a firstling) is a pu’al. No man shall sanctify it by saying, “I will give the first-born to the Lord.”⁷⁸For it already is the Lord’s from birth. This is its meaning.⁷⁹The meaning of no man shall sanctify it.