עַל־פִּ֨י הַתּוֹרָ֜ה אֲשֶׁ֣ר יוֹר֗וּךָ וְעַל־הַמִּשְׁפָּ֛ט אֲשֶׁר־יֹאמְר֥וּ לְךָ֖ תַּעֲשֶׂ֑ה לֹ֣א תָס֗וּר מִן־הַדָּבָ֛ר אֲשֶׁר־יַגִּ֥ידֽוּ לְךָ֖ יָמִ֥ין וּשְׂמֹֽאל׃
You shall act in accordance with the instructions given you and the ruling handed down to you; you must not deviate from the verdict that they announce to you either to the right or to the left.
Torah Temimah points to Sanhedrin / Sifrei.
מן הדבר. מן הדבר שהגידו לך, ולא מן הדבר שלא הגידו לך.
English: From the matter — from the matter that they told you, and not from a matter that they did not tell you.
The prohibition of deviation applies only to the specific ruling that was issued.
Derash on the verse (Sifrei) — not a formal named middah of the 13.
One is bound only by the actual decision that was announced, not by unstated implications.