I thought this was interesting history. Calvin wrote a letter to Luther. But Luther never got it:
Letter to Luther (January 21, 1545) - John Calvin - Reformed Literature
Melanchton's response:
Letter to Luther (January 21, 1545) - John Calvin - Reformed Literature
Melanchton's response:
“I have not shewn your letter to Dr. Martin, for he takes up many things suspiciously, and does not like his replies to questions of the kind you have proposed to him, to be carried round and handed from one to another. . . . . . At present I am looking forward to exile and other sorrows. Farewell. On the day upon which, 3846 years ago, Noah entered into the ark, by which God gave testimony of his purpose never to forsake his Church even when she quivers under the shock of the great sea billows.”—Melanchthon to Calvin, MSS. of Geneva, vol. 106.