Commentary Par XXVI 137-138

The recognition of the Horatian source (Ars poetica 60-63) of these verses begins with Benvenuto da Imola (DDP Benvenuto.Par.XXVI.124-129).  Here is Horace, as cited, with a translation, by Singleton (DDP Singleton.Par.XXVI.137-138):

ut silvae foliis pronos mutantur in annos,

prima cadunt; ita verborum vetus interit aetas,

et iuvenum ritu florent modo nata vigentque.

debemur morti nos nostraque....

As forests change their leaves with each year's decline,

and the earliest drop off: so with words, the old race dies,

and, like the young of human kind, the new-born bloom and thrive.

We are doomed to death -- we and all things ours.

Imbach (Imba.1996.1), p. 212, notes that Dante has cited neighboring verses in the Ars (70-71) in Conv.II.xiii.10 (for earlier notice of this fact, beginning with Steiner [DDP Steiner.Par.XXVI.136-138], see the DDP.)