This text comes from The Poetical Works of John Keats, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
No, no! go not to Lethe, neither twist
Wolf's-bane, tight-rooted, for its poisonous wine;
Nor suffer thy pale forehead to be kiss'd
By nightshade, ruby grape of Proserpine;
Make not your rosary of yew-berries,
Nor let the beetle, nor the death-moth be
Your mournful Psyche, nor the downy owl
A partner in your sorrow's mysteries;
For shade to shade will come too drowsily,
And drown the wakeful anguish of the soul.
But when the melancholy fit shall fall
Sudden from heaven like a weeping cloud,
That fosters the droop-headed flowers all,
And hides the green hill in an April shroud;
Then glut thy sorrow on a morning rose.
Or on the rainbow of the salt sand-wave,
Or on the wealth of globed peonies;
Or if thy mistress some rich anger shows,
Emprison her soft hand, and let her rave,
And feed deep, deep upon her peerless eyes.
She dwells with Beauty—Beauty that must die;
And Joy, whose hand is ever at his lips
Bidding adieu; and aching Pleasure nigh,
Turning to poison while the bee-mouth sips:
Ay, in the very temple of Delight
Veil'd Melancholy has her sovran shrine,
Though seen of none save him whose strenuous tongue
Can burst Joy's grape against his palate fine;
His soul shall taste the sadness of her might,
And be among her cloudy trophies hung.