The New Testament book that calls Noah a “preacher of righteousness” in the Noah's Ark story is 2 Peter.
Second Peter 2:5 describes God preserving Noah, whom it calls a “preacher of righteousness,” along with seven others when the ancient world was judged by the flood. The wording presents Noah as a figure who proclaimed or represented righteous conduct before the catastrophe.
This reference is separate from the Genesis narrative, which focuses on Noah, the ark, the animals, the flood, and the covenant. The phrase appears in a later Christian interpretation of those events rather than in Genesis itself.
A common mix-up is Hebrews 11, which also discusses Noah. Hebrews praises Noah's faith and says he built the ark after receiving a warning about things not yet seen, but the specific expression “preacher of righteousness” is associated with 2 Peter.