Genesis 6:3

3 Then the LORD said, “My Spirit will not contend witha humans forever, for they are mortalb ; their days will be a hundred and twenty years.”

Read Genesis 6:3 Using Other Translations

And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
Then the LORD said, "My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years."
Then the LORD said, “My Spirit will not put up with humans for such a long time, for they are only mortal flesh. In the future, their normal lifespan will be no more than 120 years.”