Who said "Who's unbeatable? The one nothing outside can shake."?

Epictetus (c. 50–135 AD). Source: Discourses 1.18.21.

What is the original Greek?

τίς οὖν ὁ ἀήττητος; ὃν οὐκ ἐξίστησιν οὐδὲν τῶν ἀπροαιρέτων. Translated from the original Greek by Spartan Surfers.

Who's unbeatable? The one nothing outside can shake.

Epictetus, Discourses 1.18.21

The source

"Who's unbeatable? The one nothing outside can shake." Epictetus said it in Discourses 1.18.21. Translated from the original Greek by Spartan Surfers.

"τίς οὖν ὁ ἀήττητος; ὃν οὐκ ἐξίστησιν οὐδὲν τῶν ἀπροαιρέτων."

Original Greek, Discourses 1.18.21. Greek: Schenkl 1916 (Teubner) via Perseus.

Who said it

Epictetus (c. 50–135 AD). Born enslaved, became the most influential Stoic teacher of his age. His student Arrian wrote down the Discourses and the Enchiridion.

Questions

Who said "Who's unbeatable? The one nothing outside can shake."?: Epictetus (c. 50–135 AD). Source: Discourses 1.18.21.
What is the original Greek?: τίς οὖν ὁ ἀήττητος; ὃν οὐκ ἐξίστησιν οὐδὲν τῶν ἀπροαιρέτων. Translated from the original Greek by Spartan Surfers.