forgive and forget - 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.
Both pardon and hold no resentment concerning a past event. For example, After Meg and Mary decided to forgive and forget their differences, they became good friends. This phrase dates from the 1300s and was a proverb by the mid-1500s. For a synonym, see let bygones be bygones.