There is a concept in Judaism called אסמכתא. This refers to certain Mitzvot that are based on the Torah, but are still considered rabbinic laws. These commandments have a different status than other commandments because they are usually based on an incident mentioned in the Torah.
In פרשת מטות, there is an example of אסמכתא. When the Torah describes the war with Midyan, we are told that there were a great deal of spoils taken after Israel’s victory with zero casualties.
They were told that all cooking utensils that were taken, needed to be dipped in a Mikva. This refers to the Mitzva of טבילת כלים.
When we purchase new dishes and pots and pans from non-Jews, they must be immersed in a Mikva. The source for this Mitzva is simply called, ״כלי מדין״.
This is classified as an אסמכתא that it is not listed among the 613 commandments, but it is an אסמכתא, that almost has the status of a Torah law.