Cite the Author and the date of publication in parentheses. You must include both the original date of publication and a republished date, if given. In the case of Aristotle's Poetics, there is no original date, since the original publication is unknown, but there will be a republished date. No date is listed as (n.d.) followed by the republished date, for example: (Aristotle, n.d./2005).
List your full citation on the reference list as author's last name, first initial, publication date in parentheses, the title (in italics), the place of publication and the publisher. In this example, it would be "Aristotle, (2005). Poetics. New York: Barnes & Noble Books."
Cite a footnote or endnote the same way you would cite on a reference list.