What was earliest use of the phrase, "white man's grave," usually used in reference to Sierra Leone?African history and literature

The term refers to the often deadly circumstances that
greeted white Westerners who ventured into the regions of Sierra Leone and other parts
of Western Africa. "White man's grave" generally concerns the deaths that were brought
upon by poor sanitation, disease and the extremes of the tropical climate. Colonists and
missionaries were hit hardest. According to one source, the term was coined in reference
to Sierra Leone, the first British West African colony. After the British abolishment of
slavery in 1772, Sierra Leone was created as a home for freed slaves, and it was
described as a

readability="5">

"comfortable establishment in a most pleasant and
fertile climate."  It was a virtual
paradise...

Missionaries and
colonists found out the hard way that this was not true. Newly relocated slaves also
died in high numbers. Malaria and yellow fever proved to be the main
causes.