Be like the bird, who
Halting in his flight
On limb too slight
Feels it give way beneath him,
Yet sings
Knowing he hath wings.

[Soyez comme l’oiseau, posé pour un instant
Sur des rameaux trop frêles,
Qui sent ployer la branche et qui chante pourtant,
Sachant qu’il a des ailes!]

Victor Hugo (1802-1885) French writer

“In the Church of *** [Dans l’eglise de ***],” Songs of Dusk [Les chants du crepuscule], #33 sec. 6 (1836)
    (Source)

Full French poem. Alternate translations:

Be like the bird that, on a bough too frail
To bear him, gaily sings!
He carols -- thought he slender branches fail:
He knows that he has wings.
[Source]

Be like the bird that seeks its short repose
And dauntless sings
Upon that bending twig, because it knows
That it has wings.
[Source]

Be like that bird, that halting in her flight
A while on boughs too slight;
Feels them give way beneath her,
And yet sings, yet sings,
Knowing that she hath wings.
[Laura Sedgwick Collins, 1890s song, "Be Like That Bird"]

Thou art like the bird
That alights and sings
Though the frail spray bends --
For he knows he has wings.
[tr. Kemble (Butler)]

Be as a bird that --
Pausing in its flight --
Alights upon a branch too slight
And feeling that it bends beneath it
Sings -- knowing it has wings.
[Source]