... for I am merciful, saith the Lord, and I will not keep anger forever. - Jeremiah 3:12
Ye have kindled a fire in mine anger, which shall burn forever. - Jeremiah 17:4
Jeremiah 3:12 in full reads, "Go and proclaim these words toward the north, and say, Return, thou backsliding Israel, saith the LORD; and I will not cause mine anger to fall upon you: for I am merciful, saith the LORD, and I will not keep anger for ever." Skeptics may leave out the conditional part, which makes all the difference in the world: It is clear by chapter 17 that the conditions have or will not been fulfilled by the subject of the anger, and moreover, clear that the "will not" here is not an eternal absolute but a matter of the present situation in line with the ancient practice of hyperbole (in which "forever" is used to stress the seriousness of the action).