Leviticus 27:28 "No taboo thing...shall be sold"

Any possession that a person declares to be "Cherem," is "taboo" and cannot be used by him anymore.

The objects or possessions considered "Cherem" are given to the priests and become theirs to use as they see fit (see Positive Mitzvah 145).

Once a person has declared his land or belongings as "Cherem," they fall into a special category.

This Negative Mitzvah forbids that person from selling them, even if he wishes to sell it to the treasury of the Beit HaMikdash.