Oresas was a Pythagorean, according to Sir William Smith, (1870).
Smith (1870) noted (p. 40):
ORESAS, a Pythagorean. A fragment of his writings is preserved in Stobaeus, Eclog. p. 105. ( Fabric. Bibl. Graec. vol. i. p. 860.) [C. P. M.]However, it has been pointed out that Stobaeus occasionally mixed up Platonism with Pythagoreanism.
References
Oresas Wikipedia(Text) CC BY-SA