Answer:
The letter from George Washington to Alexander Hamilton that you may be referring to is likely the one concerning the conflict between the states of Virginia and Maryland over navigation rights on the Potomac River, which runs between the two states.
In his letter, Washington, who was then serving as the first President of the United States, expressed his concern that the conflict could lead to armed conflict between the two states, which could have serious consequences for the young nation. Washington believed that the only way to resolve the conflict was through a compromise between the two states.
Alexander Hamilton, who was then serving as the Secretary of the Treasury, took up the task of negotiating a compromise between Virginia and Maryland. Hamilton suggested that the federal government should assume responsibility for overseeing navigation rights on the Potomac River, and that the two states should cede some of their authority to the federal government in order to resolve the conflict.
Through Hamilton's efforts, the two states eventually agreed to a compromise that established the federal government's authority over navigation on the Potomac River, and which helped to prevent armed conflict between the two states. The compromise also helped to establish the power and authority of the federal government, and played a key role in shaping the relationship between the federal government and the states in the early years of the United States.