Devarim 18:21

וכי תאמר בלבבך AND IF THOU SAY IN THINE HEART [HOW SHALL WE KNOW THE WORD WHICH THE LORD HATH NOT SPOKEN]? — you will once ask this — when Hananiah the son of Azur (the false prophet) comes and prophesies (Jeremiah 27:16) “Behold, the vessels of the Lord’s house will now shortly be brought again from Babylon”, whilst Jeremiah (the true prophet) stands and proclaims (Jeremiah 27:19—22) “concerning the pillars, and concerning the laver, and concerning the bases, and concerning the residue of the vessels [which remain in this city which Nebuchadnezzar king of Babylon took not,…]” which did not go into exile to Babylon with Jeconiah, king of Judah, “they shall be carried to Babylon [and there they shall remain]” together with Zedekiah when he will go into exile (Sifrei Devarim 178:2).

וְכִ֥י תֹאמַ֖ר בִּלְבָבֶ֑ךָ אֵיכָה֙ נֵדַ֣ע אֶת־הַדָּבָ֔ר אֲשֶׁ֥ר לֹא־דִבְּר֖וֹ יְהֹוָֽה׃

And if thou say in thy heart, How shall we know the word which the Lord has not spoken?