While imprisoned at Reading Gaol in 1897, Oscar Wilde wrote a 50,000 word letter titled De Profundis  to Lord Alfred Douglas.

De Profundis, originally titled Epistola: In Carcere et Vinculis, or Letter: In Prison and in Chains, was written between January and March of 1897. Wilde was unable to send the letter during his time incarcerated, though he was allowed to carry the letter with him once freed. 

Worldhistoryproject.org writes that, in reference to the contents of the letter, 

"He repudiates Lord Douglas for what Wilde finally sees as his arrogance and vanity; he hadn't forgotten Douglas's remark, when he was ill, 'When you are not on your pedestal you are not interesting.' He also felt redemption and fulfilment in his ordeal, realising that his hardship had filled the soul with the fruit of experience, however bitter it tasted at the time."

Robert Ross, a Canadian-British journalist, art critic, and dear friend and lover of Oscar Wilde, published De Profundis on February 11th, 1905 after renaming it from Epistola: In Carcere et Vinculis. While at Reading Gaol, Wilde gave Ross the title of personal literary executor. Upon Wilde's death in 1900, the manuscript for De Profundis was entrusted to Ross. 

While it is rumored that a copy was sent to Douglas, he refused any association, knowledge, or connection to the letter. The finalized title, De Profundis, translates to From the Depths and serves as an allusion to Psalm 130. 

https://worldhistoryproject.org/1905/de-profundis-is-published

Psalm 130 - 

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Psalm 130

A song of ascents.