Poetics (5.8-6.1)

And then as regards length, tragedy tends to fall within a single revolution of the sun or slightly to exceed that, whereas epic is unlimited in point of time;

and that is another difference, although originally the practice was the same in tragedy as in epic poetry.

The constituent parts are some of them the same and some peculiar to tragedy.

Consequently any one who knows about tragedy, good and bad, knows about epics too, since tragedy has all the elements of epic poetry, though the elements of tragedy are not all present in the epic.