Jeremiah 27:14
Therefore hearken not unto the words of the prophets that speak unto you, saying, Ye shall not serve the king of Babylon: for they prophesy a lie unto you. Therefore hearken not unto the words of the prophets that speak unto you, saying, Ye shall not serve the king of Babylon: for they prophesy a lie unto you.
The warning is to Judah not to listen to prophets who declared they would not have to serve the king of Babylon, for their prophesying was a lie and their message false. It was spoken in the controversy between Jeremiah and the false prophets during the Babylonian captivity. It belonged to Jeremiah's messages urging the people to accept the Babylonian rule that God had appointed rather than trust false assurances.
God had decreed a period of Babylonian rule, and resisting it would bring harsher punishment. The warning was part of the Lord's counsel to heed Jeremiah's messages and to follow an honorable course toward Babylon, which could have preserved respect and spared Judah from calamity.
The teaching is that people must heed God's actual warning rather than reassuring claims that contradict it.