Agree to disagree
Set aside an irreconcilable difference in order to maintain a civil dialogue.
This expression is generally thought to be of American origin and to be a variant of the earlier phrase 'agree to differ'. The latter is first cited in the Selected Letters of the master potter Josiah Wedgwood, 1785:
"The principal difficulty is to agree to differ, to agree in impartial investigation and candid argument."
Whether anyone holds that 'American origin' view strongly enough to agree to differ with the author of a 1948 edition of Notes and Queries I'm not sure, but that says that 'agree to disagree' is to be found in the text of a 1770 sermon by the English theologian John Wesley. That text shows the phrase in quotation marks, which suggests that Wesley didn't coin it himself. If that claim is correct, and I've no reason to doubt it, then 'agree to disagree' may also put into question the notion that 'agree to differ' is the earlier variant.