The ninth foundation of the Jewish faith is that the Torah is timeless and not subject to revision by human hands. The Torah was given to us by God, Who is omniscient. Since He knows all that ever is, was, or will be, it is inconceivable that the Torah wouldn’t account for the circumstances of future generations. The laws of the Torah do not get “outdated” and discarded and God certainly won’t retract the Torah and replace it with another book. (Numbers 23:19 says that God is not like a human being who might change his mind.)
God tells us not to add to or subtract from the Torah (Deuteronomy 13:11). What’s in it stays in and what’s not in it stays out. Deuteronomy 29:28 says that both we and our descendants are to keep “this Torah” – it’s the one and only, so accept no substitutes!
(Yes, there are rabbinic laws and enactments. The Torah not only empowers, it actually requires the sages of each generation to enact such things to enhance Jewish communal life or to distance people from sin. In fact, there’s a commandment to obey rabbinic laws! It’s quite clear what’s directly from the Torah and which laws were passed by the rabbis; accordingly, rabbinic laws do not violate the prohibition of adding to the Torah.)
In the Ani Maamins, this foundation is phrased, “I believe wholeheartedly that the Torah will not be changed and that God will never give another Torah.”
In Yigdal, this foundation is the line that reads “Lo yachalif ha(k)Eil v’lo yamir daso, l’olamim l’zulaso” – “God will neither replace nor alter His law, forever, in favor of anything else.”