“Life is like a bird. Whose purpose of life is only to keep flying in the open sky. Do not imprison him in the cage of your misery because he suffocates and he torments day and night in the cage. Release him to fly in the open sky because he has the courage to touch the heights of the sky. Imprisoned in a cage, he loses his confidence and forgets to fly.”
Related quotes

“Birds born in a cage think flying is an illness.”
As quoted in Investing with Impact: Why Finance is a Force for Good (2016) by Jeremy Balkin
4 Burr. Part IV., 2379.
Dissenting in Millar v Taylor (1769)

Different Seasons (1982), Rita Hayworth and Shawshank Redemption

The Dead Robin
Traits and Trials of Early Life (1836)

Homily 2. Fifty Spiritual Homilies of Saint Macarius the Egyptian, trans. Arthur J. Mason.
Disputed

“And he whose soul is flat -- the sky
Will cave in on him by and by.”
Source: Renascence and Other Poems

1880s, 1880, Letter to Theo (Cuesmes, July 1880)
Context: People are often unable to do anything, imprisoned as they are in I don't know what kind of terrible, terrible, oh such terrible cage.
I do know that there is a release, the belated release. A justly or unjustly ruined reputation, poverty, disastrous circumstances, misfortune, they all turn you into a prisoner. You cannot always tell what keeps you confined, what immures you, what seems to bury you, and yet you can feel those elusive bars, railings, walls. Is all this illusion, imagination? I don't think so. And then one asks: My God! will it be for long, will it be for ever, will it be for eternity?