Epiphanius: where does he describe Indians as the descendants of Abraham and Keturah?

The Austrian Carmelite Paulinus a Sancto Bartholomaeo in his book _"Darstellung der Brahmanisch-Indischen Götterlehre, Religionsgebräuche und bürgerliche Verfassung "_ (1797) states that Epiphanius was the first writer to link the Brahmins of India with the children of Abraham and his concubine Keturah (Genesis 25:1-4; 1 Chronicles 1:32-33), an identification later appearing in the _Zohar_ (13th century), Guillaime Postel (16th century), and Manasseh ben Israel (17th century) (as well as Newton, Voltaire and others). I have been unable to locate his source in Epiphanius' (or in other patristic) writings. Does anyone know where Epiphanius says this?