Shofetim 

שופטים

The Torah commands us to obey rulings of the court: “You shall not deviate from the matter that they will tell you” (Deuteronomy 17:11). From here, the Sages derive the general obligation to obey the words of the Sages, as God supports their statements. 

A person should not say: I am not fulfilling the ordinances and the decrees of the elders, because they are not Torah law. The Holy One, blessed be He, says to such a person: My son, you are not permitted to say so; rather, everything they decree upon you, you must fulfill, as it is stated: “On the basis of the law that they will instruct you” (17:11). Why? Because I support even their statements, not only their interpretations of the verses. <source>(<i>Tanĥuma</i>, <i>Naso</i>) </source>