Antiquities of the Jews — Book 1, Chapter 15

Abraham after this married Keturah, by whom six sons were born to him,
men of courage, and of sagacious minds: Zambran, and Jazar, and Madan,
and Madian, and Josabak, and Sous. Now the sons of Sous were Sabathan
and Dadan. The sons of Dadan were Latusim, and Assur, and Luom. The sons
of Madiau were Ephas, and Ophren, and Anoch, and Ebidas, and Eldas. Now,
for all these sons and grandsons, Abraham contrived to settle them in
colonies; and they took possession of Troglodytis, and the country of
Arabia the Happy, as far as it reaches to the Red Sea. It is related of
this Ophren, that he made war against Libya, and took it, and that his
grandchildren, when they inhabited it, called it [from his name] Africa.
And indeed Alexander Polyhistor gives his attestation to what I here
say; who speaks thus: "Cleodemus the prophet, who was also called
Malchus, who wrote a History of the Jews, in agreement with the History
of Moses, their legislator, relates, that there were many sons born to
Abraham by Keturah: nay, he names three of them, Apher, and Surim, and
Japhran. That from Surim was the land of Assyria denominated; and that
from the other two [Apher and Japbran] the country of Africa took its
name, because these men were auxiliaries to Hercules, when he fought
against Libya and Antaeus; and that Hercules married Aphra's daughter,
and of her he begat a son, Diodorus; and that Sophon was his son, from
whom that barbarous people called Sophacians were denominated."