IAGO: I am one, sir, that comes to tell you your daughter and the Moor are now making the beast with two backs.

Shakespeare
William Shakespeare (1564–1616) English dramatist and poet
Othello, Act 1, sc. 1, l. 129ff (1.1.129-131) (1603)
    (Source)

Speaking to Desdemona's father, the senator Brabantio. Earliest recorded use of "beast with two backs" in English; though Rabelais used it in Gargantua and Pantagruel (c. 1532), but that is not known to have been translated to English until the late 17th Century. (More info here).