Jeremiah 27:15
For I have not sent them, saith the LORD, yet they prophesy a lie in my name; that I might drive you out, and that ye might perish, ye, and the prophets that prophesy unto you. For I have not sent them, saith the LORD, yet they prophesy a lie in my name; that I might drive you out, and that ye might perish, ye, and the prophets that prophesy unto you.
The verse belongs to the account of Jeremiah's letters to the captives and the answering letters of the false prophets, standing within the controversy between true and false prophecy during the Babylonian captivity. The prophets it condemns promised the nations and Judah that they would escape Babylonian rule and that its end would come speedily, urging resistance to Babylon, yet they were not sent by God but spoke lies in His name. Against their message God had commanded submission to Babylon's temporary rule, with quiet submission bringing peace. That submission included avoiding entangling alliances with Egypt and maintaining friendly relations with Babylon.
Listening to the false prophets and resisting that command would lead Zedekiah and the exiles to rebel, bringing suffering, disaster, and tighter restrictions. The people would be driven from their land and perish together with the prophets who misled them. In the same way Judah and the prophets urging resistance would be brought to destruction for heeding a false message spoken in God's name.
More generally the verse shows that claims made in God's name are not necessarily sent by Him, since false speakers can present their own opinions as truth while leading people away from truth toward ruin. In that sense it applies to the confusion after the great disappointment, when conflicting opinions were presented as the message of truth, warning seekers not to believe what the Lord had not sent. It also applies to those who advocate enterprises opposed to God's word, warning that they are not sent by Him and that joining their work even in a small way puts God's people on dangerous ground and may draw them away from the work and warnings He has given.