Numbers 23:20

Behold, I have received commandment to bless, and He hath blessed; and I cannot reverse it. The unchangeability of the divine counsels is a necessary consequence of the divine faithfulness, as an expression of the essence of the Lord. The blessing which He had put into the mouth of Balaam after the first sacrifice could not be canceled, and the soothsayer was not in a position to cancel it, much as he personally might be inclined to do so.