We were born for cooperation, like feet, like hands, like eyelids, like the rows of upper and lower teeth. So to work against each other is contrary to nature; and resentment and rejection count as working against someone.

[γεγόναμεν γὰρ πρὸς συνεργίαν ὡς πόδες, ὡς χεῖρες, ὡς βλέφαρα, ὡς οἱ στοῖχοι τῶν ἄνω καὶ κάτω ὀδόντων. τὸ οὖν ἀντιπράσσειν ἀλλήλοις παρὰ φύσιν: ἀντιπρακτικὸν δὲ τὸ ἀγανακτεῖν καὶ ἀποστρέφεσθαι.]

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

Meditations [To Himself; Τὰ εἰς ἑαυτόν], Book 2, ch. 1 (2.1) [tr. Gill (2013)]
    (Source)

(Source (Greek)). Alternate translations:

For we are all born to be fellow-workers, as the feet, the hands, and the eyelids; as the rows of the upper and under teeth: for such therefore to be in opposition, is against nature; and what is it to chafe at, and to be averse from, but to be in opposition?
[tr. Casaubon (1634), 1.15]

For we are all made for mutual Assistance, no less than the Parts of the Body are for the Service of the whole; From whence it follows that Clashing and Opposition is perfectly Unnatural: Now such an unfriendly Disposition is imply'd in Resentment and Aversion.
[tr. Collier (1701)]

We were formed by nature for mutual assistance, as the two feet, the hands, the eye¬ lids, the upper and lower rows of teeth. Opposition to each other is contrary to nature: All anger and aversion is an opposition.
[tr. Hutcheson/Moor (1742)]

For we are all born for our mutual assistance; as the hands and feet, and every part of the human body, are for the service of the whole; to thwart and injure each other, therefore, is contrary to nature. Now injuries and hostilities are generally the consequence of hatred and resentment.
[tr. Graves (1792)]

For we are made for co-operation, like feet, like hands, like eyelids, like the rows of the upper and lower teeth. To act against one another, then, is contrary to nature; and it is acting against one another to be vexed and to turn away.
[tr. Long (1862)]

For we are all made for mutual assistance, as the feet, the hands, and the eyelids, as the rows of the upper and under teeth, from whence it follows that clashing and opposition is perfectly unnatural. Now such an unfriendly disposition is implied in resentment and aversion.
[tr. Collier/Zimmern (1887)]

For we are made for co-operation, like the feet, the hands, the eyelids, the upper and the lower rows of teech. To thwart one another is contrary to nature; and one form of thwarting is resentment and estrangement.
[tr. Rendall (1898)]

For we are made by nature for mutual assistance, like the feet, the hands, the eyelids, the upper and lower rows of teeth. It is against nature for men to oppose each other; and what else is anger and aversion?
[tr. Hutcheson/Chrystal (1902)]

For we have come into being for co-operation, as have the feet, the hands, the eyelids, the rows of upper and lower teeth. Therefore to thwart one another is against Nature; and we do thwart one another by shewing resentment and aversion.
[tr. Haines (Loeb) (1916)]

For we have come into the world to work together, like feet, like hands, like eyelids, like the rows of upper and lower teeth. To work against one another therefore is to oppose Nature, and to be vexed with another or to turn away from him is to tend to antagonism.
[tr. Farquharson (1944)]

For he and I were born to work together, like a man’s two hands, feet, or eyelids, or like the upper and lower rows of his teeth. To obstruct each other is against Nature’s law -- and what is irritation or aversion but a form of obstruction?
[tr. Staniforth (1964)]

For we have come into being to work together, like feet, hands, or eyelids, or the two rows of teeth in our upper and lower jaws. To work against one another is therefore contrary to nature; and to be angry with another and turn away form him is surely to work against him.
[tr. Hard (1997 ed.)]

We were born to work together like feet, hands, and eyes, like the two rows of teeth, upper and lower. To obstruct each other is unnatural. To feel anger at someone, to turn your back on him: these are obstructions.
[tr. Hays (2003)]

We were born for cooperation, like feet, like hands, like eyelids, like the rows of upper and lower teeth. So to work in opposition to one another is against nature: and anger or rejection is opposition.
[tr. Hammond (2006)]

For we have been made for cooperation, just like the feet, the hands, the eyelids, and the upper and lower teeth. To hinder one another, then, is contrary to Nature, and this is exactly what happens when we are angry and turn away from each other.
[tr. Needleman/Piazza (2008)]

For we have come into being to work together, like feet, hands, eyelids, or the two rows of teeth in our upper and lower jaws. To work against one another is therefore contrary to nature; and to be angry with another person and turn away from him is surely to work against him.
[tr. Hard (2011 ed.)]

For both they and I need each other. To act against them would be to act against myself. And to become angry and turn away from them is also to act against them.
[tr. McNeill (2019)]