E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
All Souls Day.
The 2nd of November, so called because the Roman Catholics on that day seek by prayer and almsgiving to alleviate the sufferings of souls in purgatory. It was first instituted in the monastery of Clugny, in 993.
According to tradition, a pilgrim, returning from the Holy Land, was compelled by a storm to land on a rocky island, where he found a hermit, who told him that among the cliffs of the island was an opening into the infernal regions through which huge flames ascended, and where the groans of the tormented were distinctly audible. The pilgrim told Odilo, abbot of Clugny, of this; and the abbot appointed the day following, which was November 2nd, to be set apart for the benefit of souls in purgatory.