put words in someone's mouth
Tell what someone should say, as in Give Janey a chance to answer my question; don't put words in her mouth. This graphic term appeared in the Bible (II Samuel 14:3): “So Joab put words in her mouth.” Also see take the words out of one's mouth.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.