In a word, there is only one thing here worth the minding, and that is, to be true and just, and to show benevolence, even to the untrue and unjust.

[Ἓν ὧδε πολλοῦ ἄξιον, τὸ μετ᾿ ἀληθείας καὶ δικαιοσύνης εὐμενῆ τοῖς ψεύσταις καὶ ἀδίκοις διαβιοῦν.]

Marcus Aurelius (AD 121-180) Roman emperor (161-180), Stoic philosopher

Meditations [To Himself; Τὰ εἰς ἑαυτόν], Book 6, ch. 47 (6.47) (AD 161-180) [tr. Collier/Zimmern (1887)]
    (Source)

(Source (Greek)). Alternate translations:

One thing there is, and that only, which is worth our while in this world, and ought by us much to be esteemed; and that is, according to truth and righteousness, meekly and lovingly to converse with false, and unrighteous men.
[tr. Casaubon (1634), 6.42]

In a word. There's only one thing here worth the minding; And that is, not to imitate the Degeneracy of Mortals: But to be True, Honest, and Good-natur'd, even amongst Knaves, and Sharpers.
[tr. Collier (1701)]

The one thing valuable in this life, is, to spend it in a steady course of truth, justice, and humanity, toward even the false and unjust.
[tr. Hutcheson/Moor (1742)]

In short, there is nothing here much worth our attention, but to act on all occasions with a regard to truth and justice, and to live peaceably even with those who act with fraud and injustice.
[tr. Graves (1792), 6.41]

One thing here is worth a great deal, to pass thy life in truth and justice, with a benevolent disposition even to liars and unjust men.
[tr. Long (1862)]

Here one thing is of real worth, to live out life in truth and justice, with charity even to the false and the unjust.
[tr. Rendall (1898)]

The one precious thing in life is to spend it in a steady course of truth and justice, with kindliness even for the false and the unjust.
[tr. Hutcheson/Chrystal (1902)]

One thing on earth is worth much -- to live out our lives in truth and justice, and in charity with liars and unjust men.
[tr. Haines (Loeb) (1916)]

One thing here is of great price, to live out life with truth and righteousness, gracious to liars and to the unrighteous.
[tr. Farquharson (1944)]

In this life one thing only is of precious worth: to live out one's days in truthfulness and fair dealing, and in charity even with the false and unjust.
[tr. Staniforth (1964)]

In this world there is only one thing of real value, to pass our days in truth and justice, and yet be gracious to those who are false and unjust.
[tr. Hard (1997 ed.)]

The only thing that isn’t worthless: to live this life out truthfully and rightly. And be patient with those who don't.
[tr. Hays (2003)]

In this world there is only one thing of value, to live out your life in truth and justice, tolerant of those who are neither true nor just.
[tr. Hammond (2006)]

In this world there is only one thing of real value, to pass our days in truth and justice, and yet be gracious to those who are false and unjust.
[tr. Hard (2011 ed.)]

So there is one thing that is of most value: to live out your life in truth and justice and be kind to those who are false and unjust.
[tr. Gill (2013)]

So one thing is worth much: to keep on living with truth and justice and in good will even among liars and unjust men.
[tr. @sentantiq (2019)]