mark my words
Pay attention to what I say, as in Mark my words, that man is not to be trusted. This admonition first appeared in Miles Coverdale's 1535 translation of the Bible (Isaiah 28:23).
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.