The prophets that have been before me - Namely, Joel, Amos, Hosea, Micah, Zephaniah, Nahum, Habakkuk, and others; all of whom denounced similar evils against a corrupt people.
Albert Barnes
Notes on the Whole Bible
Verses 6-9
Jeremiah‘s own wishes concurred with Hananiah‘s prediction, but asserts that that prediction was at variance with the language of the older prophets.
Jeremiah 28:9
Then shall the prophet … - Or, “shall be known as the prophet whom the Lord hath truly sent.”
Matthew Henry
Concise Bible Commentary
Hananiah spoke a false prophecy. Here is not a word of good counsel urging the Jews to repent and return to God. He promises temporal mercies, in God's name, but makes no mention of the spiritual mercies which God always promised with earthly blessings. This was not the first time Jeremiah had prayed for the people, though he prophesied against them. He appeals to the event, to prove Hananiah's falsehood. The prophet who spake only of peace and prosperity, without adding that they must not by wilful sin stop God's favours, will be proved a false prophet. Those who do not declare the alarming as well as the encouraging parts of God's word, and call men to repentance, and faith, and holiness, tread in the steps of the false prophets. The gospel of Christ encourages men to do works meet for repentance, but gives no encouragement to continue in sin.
Prophet be known. To gain favor the false prophet satisfied and deceived the people with promises of an assured prosperity, in opposition to the predictions of “evil, and of pestilence” (see v.8) given by the true prophet (see on ch.14:13). Jeremiah knew he could rest his case on the issue of the fulfillment or nonfulfillment of his prophecies (see Deut. 18:20-22).