Catechism of the Catholic Church §1958 — excerpt
The natural law is immutable and permanent throughout the variations of history; it subsists under the flux of ideas and customs and supports their progress.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: GS 10 · St. Augustine, Conf. 2, 4, 9: PL 32, 678