Where does it say in the Qur'an that its rules and rituals are timeless and meant for all times in the future?
After many rules you will find the statement "these are the limits set by God, do not transgress them" such as some divorce rules:
2:229 Divorce is twice. Then, either keep [her] in an acceptable manner or release [her] with good [treatment]. And it is not lawful for you to take anything of what you have given them unless both fear that they will not be able to keep [within] the limits of God. But if you fear that they will not keep [within] the limits of God, then there is no blame upon either of them concerning that which she ransoms herself by.
These are the limits of God, so do not transgress them. And whoever transgresses the limits of God - it is those who are the wrongdoers. .2:232
And when you divorce women and they have reached their term, do not prevent them from remarrying their [former] husbands if they agree amongst themselves on an acceptable basis.
That is instructed to whoever of you believes in God and the Last Day. That is better for you and purer, and God knows and you do not know.
65:1
O prophet, when you divorce women, divorce them for their waiting period and keep count of the waiting period, and fear God, your Lord. Do not turn them out of their houses, nor should they leave unless they are committing a clear immorality.
And those are the limits [set by] God. And whoever transgresses the limits of God has certainly wronged himself. You do not know; perhaps God will bring about a [different] matter after that.
65:2
And when they have reached their term, either retain them according to acceptable terms or part with them according to acceptable terms. And bring two just witnesses from among you and establish the testimony for God.
That is instructed to whoever should believe in God and the Last Day. And whoever fears God - He will make a way out for him
Fasting
2:187 It has been made lawful for you to go to your wives the night [preceding] fasting. They are clothing for you and you are clothing for them. God knows that you used to deceive yourselves, so He turned towards you and forgave you. So now, have relations with them and seek that which God has decreed for you. And eat and drink until the white thread of dawn becomes clear to you from the black thread [of night]. Then complete the fast until the night. And do not have relations with them as long as you are devoted in the mosques.
These are the limits [set by] God, so do not approach them. Thus, God makes His verses clear to the people so that they may fear [Him].How to make your will
4:12 And for you is half of what your wives leave if they have no child. But if they have a child, for you is one fourth of what they leave, after any will they [may have] made or debt. And for [the wives] is one fourth if you have no child. But if you have a child, then for them is an eighth of what you leave, after any will you [may have] made or debt. And if a man or woman leaves neither ascendants nor descendants but has a brother or a sister, then for each one of them is a sixth. But if they are more than that, they are partners in a third, after any will which was made or debt, as long as there is no detriment [caused]. [This is] a will from God, and God is Knowing and Forbearing.
4:13
These are the limits [set by] God, and whoever obeys God and His messenger will be admitted by Him to Gardens [in Paradise] in which rivers flow beneath them, abiding eternally therein; and that is the great success.
4:14
And whoever disobeys God and His messenger and transgresses His limits - He will put him into the Fire to abide eternally therein, and he will have a humiliating punishment.
General description of what a believer is
9:112 It is the believers who repent, who are devoted to worship, who praise their Lord, who fast, who bow down and prostrate themselves, who encourage good and forbid evil, and
who observe the limits set by God. And give good news to the believers.
