On October 17, 1823, Monroe wrote a letter to his former teacher and good friend, Thomas Jefferson. Not an usual occurrence, but in this case, Monroe was asking for advice on a foreign policy matter he was considering. That foreign policy matter would become the Monroe Doctrine, which Monroe delivered in his annual message to Congress on December 2, 1823.
This article from Politico will tell you what Jefferson’s advice was. You can read the text of the Doctrine in the Research section of our website.