Who said "Write it on your soul, not on paper."?

Antisthenes (c. 446–366 BC). Source: Diogenes Laertius 6.5.

What is the original Greek?

ἔδει γάρ, ἔφη, ἐν τῇ ψυχῇ αὐτὰ καὶ μὴ ἐν τοῖς χαρτίοις καταγράφειν. Translated from the original Greek by Spartan Surfers.

Antisthenes, Diogenes Laertius 6.5

"Write it on your soul, not on paper." Antisthenes said it in Diogenes Laertius 6.5. Translated from the original Greek by Spartan Surfers.

"ἔδει γάρ, ἔφη, ἐν τῇ ψυχῇ αὐτὰ καὶ μὴ ἐν τοῖς χαρτίοις καταγράφειν."

Original Greek, Diogenes Laertius 6.5. Greek: Hicks 1925 Loeb text via Perseus.

Antisthenes (c. 446–366 BC). Student of Socrates and forerunner of the Cynics.

Who said "Write it on your soul, not on paper."?: Antisthenes (c. 446–366 BC). Source: Diogenes Laertius 6.5.
What is the original Greek?: ἔδει γάρ, ἔφη, ἐν τῇ ψυχῇ αὐτὰ καὶ μὴ ἐν τοῖς χαρτίοις καταγράφειν. Translated from the original Greek by Spartan Surfers.