Recently，I read an article named “From Schwarz to Pick to Ahlfors and Beyond”, where it says that
The standard proof (By Maximum Modulus Principle) of the Schwarz Lemma is not the proof that Schwarz himself originally gave.
So I want to know the original proof by Schwarz. However, I searched for it for a long time, but failed. Hence, I want to ask you for help, or you can give me another proof other than by maximum modulus principle.