This is all I had to say on friendship. One piece of advice on parting. Make up your minds to this. Virtue (without which friendship is impossible) is first; but next to it, and to it alone, the greatest of all things is Friendship.

[Haec habui de amicitia quae dicerem. Vos autem hortor ut ita virtutem locetis, sine qua amicitia esse non potest, ut ea excepta nihil amicitia praestabilius putetis.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Laelius De Amicitia [Laelius on Friendship], ch. 27 / sec. 104 (44 BC) [tr. Shuckburgh (1909)]
    (Source)

Original Latin. Alternate translations:

Such are the remarks I had to make on friendship. But as for you, I exhort you to lay the foundations of virtue, whithout which friendship can not exist, in such a matter that, with this one exception, you may consider that nothing in the world is more excellent than friendship.
[tr. Edmonds (1871)]

I had these things to say to you about friendship; and I exhort you that you so give the foremost place to virtue without which friendship cannot be, that with the sole exception of virtue, you may think nothing to be preferred to friendship.
[tr. Peabody (1887)]

This is all that I had to say about friendship; but I exhort you both so to esteem virtue (without which friendship cannot exist), that, excepting virtue, you will think nothing more excellent than friendship.
[tr. Falconer (1923)]