Yep, it's in there. The work is actually called 'Ars Poetica' of 'Epistle to the Pisos'. Starting at Line 70, you'll find:
Multa renascentur quae iam cecidere, cadentque
quae nunc sunt in honore vocabula, (si volet usus,
quem penes arbitrium est et ius et norma loquendi.)
That translates to:
Many words that are now unused will be rekindled,
Many fade now well-regarded, (if usage wills it so,
to whom the laws, rules, and control of language belong.)
Parentheses not in text - added to show additional text after the quoted part.
Horace is actually writing about words themselves. He's saying that old words will be revived and used again, while current words will fall out of use. Remember, he's writing about the mechanics of poetry.
The phrasing was so well-constructed that the original quote was modified slightly by leaving out any reference to words (All you have to do in the Latin is drop one word - 'vocabula.' - to do the same.), and you had something that could apply to many things.