During Joseph Haydn’s 1794–95 visit to London, his Symphony No. 102 was premiered at the King’s Theatre, conducted by the composer himself. The curious audience pressed eagerly towards the stage, hoping to catch a closer glimpse of the master, unaware that this instinct would prove life-saving.
During the concert, the theatre’s enormous chandelier came loose and shattered, falling onto the part of the auditorium where, by that time, no one was seated, for everyone had gathered near Haydn. Miraculously, no one was injured.
The stunned silence was soon broken by exclamations of, “Miracle! Miracle!”
According to Haydn’s biographer Albert Christoph Dies, it was from this incident that the symphony came to be referred to, for a time in London, as “The Miracle.”
Why the nickname later became associated not with Symphony No. 102 but with Symphony No. 96 remains a mystery. The chandelier miracle undoubtedly occurred, and the Morning Chronicle reported it the following day.

Source: Christopher Hogwood: Haydn’s Visit to England. Thames & Hudson, 1980