Khomeini's letter to Mikhail Gorbachev
On 7 January 1989, Ruhollah Khomeini, supreme leader of Iran, sent a letter to Mikhail Gorbachev, the General Secretary of the Communist Party of the Soviet Union. This letter was Khomeini's only written message to a foreign leader.
Source: Wikipedia — Khomeini's letter to Mikhail Gorbachev (CC BY-SA 4.0)