But if I err in this Opinion, that the Soul of Man is immortal, sure it is a pleasing Error, so pleasing that I can never shake it off while I live.

[Quod si in hoc erro, qui animos hominum immortalis esse credam, libenter erro nec mihi hunc errorem, quo delector, dum vivo, extorqueri volo.]

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

De Senectute [Cato Maior; On Old Age], ch. 23 / sec. 85 (23.85) (44 BC) [tr. J. D. (1744)]
    (Source)

(Source (Latin)). Alternate translations:

But if it be in erroure and oute of trouthe aftir the doctryne and scole of Epycures by cause that I beleve that the soules be undedly and Immortelle perdurable and evirlastyng I answere you that this errour pleasith me and I consente me in it right gladly and as long tyme as I lyve I wille not that any philosopher nor any othir of what condicyon that evir he be take awey fro me this erroure wherin I delyte me.
[tr. Worcester/Worcester/Scrope (1481)]

And if I do err because I think that the souls of men be immortal, verily I am well contented in the same error still to continue, and as long as I live I will never renounce nor recant the same, wherein I take such singular pleasure and comfort.
[tr. Newton (1569)]

But if I do erre that the soules of men bee immortall, I do err willingly, neither will I while I live be wrested from mine opinion wherein I am delighted.
[tr. Austin (1648), ch. 24]

My hope's, if this assurance hath deceiv'd,
(That I Man's Soul Immortal have believ'd)
And if I erre, no Pow'r shall dispossess
My thoughts of that expected happiness.
[tr. Denham (1669), Part 4]

But if I should be mistaken in this Belief, that our Souls are immortal, I am however pleased and happy in my Mistake; nor while I live, shall it ever be in the Power of Man, to beat me out of an Opinion, that yields me so solid a Comfort, and so durable a Satisfaction.
[tr. Logan (1744)]

And after all should this my firm persuasion of the soul's immortality prove to be a mere delusion, it is at least a pleasing delusion, and I will cherish it to my latest breath.
[tr. Melmoth (1773)]

But if I err in this, that I believe the soules of men to be immortal, I err willingly, nor do I wish this error to be wrested from me while I live.
[Cornish Bros. ed. (1847)]

And if I am wrong in this, that I believe the souls of men to be immortal, I willingly delude myself : nor do I desire that this mistake, in which I take pleasure, should be wrested from me as long as I live.
[tr. Edmonds (1874)]

But if I err in believing that the souls of men are immortal, I am glad thus to err, nor am I willing that this error in which I delight shall be wrested from me so long as I live.
[tr. Peabody (1884)]

But if I am wrong in thinking the human soul immortal, I am glad to be wrong; nor will I allow the mistake which gives me so much pleasure to be wrested from me as long as I live.
[tr. Shuckburgh (1895)]

But if in thinking souls immortal thus,
I am in error, I confess to you,
It is an error that I glory in,
And being so pleasant, I would not desire
To lose it while I live.
[tr. Allison (1916)]

And if I err in my belief that the souls of men are immortal, I gladly err, nor do I wish this error which gives me pleasure to be wrested from me while I live.
[tr. Falconer (1923)]

Even if I am mistaken in my belief that the soul is immortal, I make the mistake gladly, for the belief makes me happy, and is one which as long as I live I want to retain.
[tr. Grant (1960, 1971 ed.)]

And if I am deluded in believing that the soul of man is immortal, then I am glad to be deluded, and I hope no one, as long as I live, will ever wrench this delusion from me.
[tr. Copley (1967)]

But if I am mistaken in this belief of mine that the souls of men are immortal, then I am happy to be mistaken; but as long as I am still alive, I have no wish to be disabused of my mistake.
[tr. Cobbold (2012)]

I may be wrong in my belief in the immorality of the spirit: there are philosophers who think I am. I like my faith and I don't want to lose it.
[tr. Gerberding (2014)]

And if it is an error of mine to imply
That man is endowed with immortal soul,
I err with pleasure and promptly console
Myself as long as I am alive and spry.
[tr. Bozzi (2015)]

And if I’m wrong in my belief that souls are immortal, then gladly do I err, for this belief, which I hope to maintain as long as I live, makes me happy.
[tr. Freeman (2016)]