Deuteronomy 15:19

כל הבכור ... תקדיש ALL THE FIRSTLING MALES … THOU SHALT SANCTIFY [UNTO THE LORD] — But in another passage (Leviticus 27:26) it states, “[Only the firstborn of the beasts …] one shall not sanctify it”? How can these be reconciled? The latter passage means: he must not dedicate it as a different sacrifice (i.e. offer it as an עולה or שלמים instead of as a בכור), whilst here it teaches that it is a duty to say: “Thou art holy as a firstborn!” Another comment is: It is impossible to say that “thou shalt sanctify” is to be taken literally, for it already states in another passage “one shall not sanctify it”; it is, on the other hand, also impossible to take “one shall not sanctify it” literally, since it states “thou shalt sanctify it”. How can these be reconciled? In the following manner: by taking תקדיש in our verse to imply: “thou mayest dedicate” so far as the dedication of its value (הקדש עלוי) is concerned, and then he must give a sum corresponding to the טובת הנאה in it to the Temple treasury, but you must not dedicate it as far as the altar is concerned (i.e. dedicate it as any sacrifice other than as a בכור) (Arakhin 29a: cf. Sifrei Devarim 124:4). לא תעבד בבכור שורך ולא תגז וגו׳ THOU SHALT NOT WORK WITH THE FIRSTLING OF THY HERD, NOR SHEAR [THE FIRSTLING OF THY FLOCK] — The converse case also (working with the firstborn sheep and using the hair of the firstborn calf) have our Rabbis derived to be forbidden, but Scripture merely speaks of what usually occurs (Sifrei Devarim 124:6; Bekhorot 25a).

כׇּֽל־הַבְּכ֡וֹר אֲשֶׁר֩ יִוָּלֵ֨ד בִּבְקָרְךָ֤ וּבְצֹֽאנְךָ֙ הַזָּכָ֔ר תַּקְדִּ֖ישׁ לַיהֹוָ֣ה אֱלֹהֶ֑יךָ לֹ֤א תַעֲבֹד֙ בִּבְכֹ֣ר שׁוֹרֶ֔ךָ וְלֹ֥א תָגֹ֖ז בְּכ֥וֹר צֹאנֶֽךָ׃

All the firstling males that come of thy herd and of thy flock thou shalt sanctify to the Lord thy God: thou shalt do no work with the firstling of thy bullock, nor shear the firstling of thy sheep.