mark my words - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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).