pentateuch chumash - Is there a mention of the Oral Torah in the Written Torah?

Is there an explicit mention mention of the Oral Torah in the Chumash? If not, why not?

Answer

There are a few hints to the Oral Torah in the Chumash, but nothing explicit.

One of these is found in Devarim 12:21:

וְזָבַחְתָּ מִבְּקָרְךָ וּמִצֹּאנְךָ אֲשֶׁר נָתַן יְהֹוָה לְךָ כַּאֲשֶׁר צִוִּיתִךָ

you may slaughter of your cattle and of your sheep, which the Lord has given you, as I have commanded you

The problem is that we don't find any command of how to slaughter in the Torah. So the Talmud writes (Chulin 28a):

דתניא רבי אומר וזבחת כאשר צויתיך מלמד שנצטוה משה על הושט ועל הקנה ועל רוב אחד בעוף ועל רוב שנים בבהמה

As was taught in a braysa, Rebbi (R Yehudah HaNassi) says, "וזבחת כאשר צויתיך" teaches that Moshe was taught (orally) on the esophagus and trachea (that they need to be cut so that the slaughter is kosher), and on רוב אחד בעוף (that most of one of the above need to be cut for the slaughter of birds to be kosher) and on רוב שנים בבהמה (that most of the food pipe and most of the wind pipe need to be cut for the slaughter of animals to be kosher)

This is also brought down by the Simlah Chadasha (1:1), and discussed in my question here.