הלכה על חולין 55:39

All the laws of Shechita were told to Moshe Rabbenu orally at Sinai like all of the Oral law, as it is written " you may slaughter any of the cattle or sheep that the LORD gives you, as I have instructed you (Deuteronomy.12.21)" This mitzvah is apart of the oral tradition. It is taught in a baraita: "Rabbi Yehuda HaNasi says: The Torah states: “And you shall slaughter of your herd and of your flock, which the Lord has given you, as I have commanded you” (Deuteronomy 12:21). This verse teaches that Moses was previously commanded about the halakhot of slaughter, even though they are not written explicitly in the Torah. He was commanded about cutting the gullet and about cutting the windpipe, and about the requirement to cut the majority of one siman for a bird, and the majority of two simanim for an animal." (According to Tosfot), Rebbe finds an allusion to this in the word "כאשר". The "Alef" (achad) alludes to one siman in a bird, the "Shin" (Shtayim) alludes to two simanim in an animal, and the "Resh" (Rubo) alludes to the majority of one is like the whole. Furthermore, the word כאשר is the reverse acrostic of רובו של אחד כמוהו the majority of one is like the whole.

From the laws of the commandment is that which they, may their memory be blessed, said (Temurah 32b) that one who consecrates an unblemished beast for the altar and a blemish develops on it and it becomes disqualified, behold it is appraised and redeemed and he brings another beast instead of it. And about this is it stated (Leviticus 27:11), "And if it is any impure animal from which shall not be sacrificed to the Lord, he shall appraise the beast, etc." - as so did it come in the received traditional understanding, that Scripture expressed [this] with the expression of "impure." And whether a man consecrated a pure animal for the altar and a blemish developed upon it, as we said - or an impure [one] for the [Temple] upkeep - it requires being placed in front of the priest, as it is stated, "and he shall place the beast in front of the priest," and he appraises it. And if it died before it is appraised and redeemed, we do not appraise it and we do not redeem it after it died. But if he slaughtered two (the esophagus and the trachea) or the majority of two - even though it is like dead regarding slaughter, as it is established for us (Chullin 28a), as so was Moshe commanded about the majority of one with fowl and the majority of two with a beast - behold, it is living regrading appraisals. And [so] he brings it in front of the priest, and he appraises it. And the rest of its details are in [various] places in Temurah and Meilah (see Mishneh Torah, Laws of Substitution 4).