I was searching for where in Lucretius he talks about impermanence (Google AI says in Book 3) and happened on this introductory level article regarding "death is nothing to us", which contains excerpts from Luctretius:
Why Death is Nothing to Fear: Lucretius and Epicureanism | Philosophy Break
In his epic poem De Rerum Natura (On The Nature of Things), Roman philosopher Lucretius outlines why, even though there may be no overarching design to life,…
philosophybreak.com
(For the text references, I don't see what translation he is using, and so perhaps he has created a kind of paraphrasing of the text).