The Zohar (quoted here), says that the souls that are undergoing the painful cleansing process of Gehenom (purgatory, hell, see here), are given respite during the 24 hours of Shabbat.
This idea is brought in Halacha as well.
Does the same apply to proper Jewish Holidays (i.e. when work is forbidden), such as Pesach, Shavuot, and Sukkot?