cart before the horse, put the
Reverse the proper order of things or events, as in Don't put the cart before the horse and give away the punch line. This expression has been used since antiquity but was first recorded in English in 1520.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.