Jeremiah 28:9
The prophet which prophesieth of peace, when the word of the prophet shall come to pass, then shall the prophet be known, that the LORD hath truly sent him. The prophet which prophesieth of peace, when the word of the prophet shall come to pass, then shall the prophet be known, that the LORD hath truly sent him.
The test given is for a prophet who foretells peace: only when his word comes to pass is he known to have been truly sent by the Lord. It belongs to the account in Jeremiah 27-29 involving the letters to the captives in Babylon and the controversy between true and false prophets. Jeremiah directed this test to Hananiah's promise of peace and speedy deliverance, which opposed Jeremiah's warning.
Hananiah predicted that Babylon's yoke would be broken and the exiles and the temple vessels would be restored within two years, against Jeremiah's warning of continued subjection. Coming events would reveal which prophet spoke truly. Hananiah's death in the seventh month fulfilled Jeremiah's prediction made in the fifth month and confirmed that Jeremiah's message was from the Lord.
Jeremiah's warning was supported by earlier judgments that had fulfilled the warnings of true prophets. Predictions of peace can be used to quiet the people's fears and to win favor with those in power. Promising prosperity when God has declared judgment reassures people in their sins and strengthens them to resist the true prophet's counsel.