Though this is the proposition universally associated by tradition with the name of Pythagoras, no really trustworthy evidence exists that it was actually discovered by him.

Heath, Thomas. A History of Greek Mathematics, Vol. 1. Oxford at the Clarendon Press, 1921 , quoted from Bhaskar Kamble, The Imperishable Seed: How Hindu Mathematics Changed the World and why this History was Erased, Garuda Prakashan Private Limited, 2022 ISBN 9798885750189 (Heath 1921: 144)