Abdul Kader of the Senegalese Basin
In the late 18th Century in Futa Toro, in what is now Senegal, Abdul Kader Kane, the religious leader of the area who defeated the locals and created a Theocracy, opposed to the transatlantic slave trade and wrote a letter to the French warning them to desist from it.
Also known as King Almammy, Abdul Kader ruled from 1776 when he was barely 50 years old to 1806 when he died after he was defeated and captured in an attack on the Wolof states of Cayor and Waalo around 1797.
Besides defeating several kingdoms in the region, he also sent a letter to the French threatening death to anyone who tried to procure slaves in his territory.
He signed an agreement with Louis XVI of France in 1785, which regulated French trade with the state of Futa (i.e., charged French vessels tariffs), and outlawed the sale of Muslims into the Atlantic Slave System, cites rowan.edu.
Read the letter below he wrote to Commandant Blanchot in a French coastal fort Saint-Louis in present-day Martinique in March 1789.
We are warning you that all those who will come to our land to trade [in slaves] will be killed and massacred if you do not send our children back. Would not somebody who was very hungry abstain from eating if he had to eat something cooked with his blood? We absolutely do not want you to buy Muslims under any circumstances. I repeat that if your intention is to always buy Muslims you should stay home and not come to our country anymore. Because all those who will come can be assured that they will lose their life.
Signed, Al-ammamy