When the Jewish people celebrated the Dedication of the First Temple built by King Solomon, the seven days of its dedication during Tishrei also fell on Yom Kippur. That Yom Kippur, the Temple dedication ceremony continued like during the other days: the sacrifices were offered and the people ate and drank.
The gemara says about this: Rabbi Franich said in the name of Rabbi Jochanan: That year the Jews did not keep Yom Kippur. They became worried and said, “Maybe we will incur death for this?” A voice rung out from heaven and said, “You are all worthy of the Hereafter.”
The Jewish people were worried that perhaps they should have made do with just offering sacrifices instead of also celebrating with food and drink as during the other days of the Temple dedication, but a heavenly voice calmed them and told them they had done no sin. Why did King Solomon and the sages of his generation decide that there was no need to fast that year? Apparently the holiness that was generated at the dedication of the first permanent House of G-d was so great that it was equal to standing before G-d and having their sins forgiven even without fasting. This is how the Book of Chronicles describes the great spiritual exaltation during the dedication of the Temple:
“And when Solomon finished praying, the fire descended from heaven and consumed the burnt offerings and the sacrifices, and the glory of the L-rd filled the House. And the priests could not enter the House of the L-rd, because the glory of the L-rd filled the House of the L-rd. And all the Children of Israel saw the descent of the fire, and the glory of the L-rd on the House, and they kneeled on their faces to the ground on the floor, and they prostrated themselves and [said]: “Give thanks to the L-rd, for He is good, for His loving-kindness is eternal.” (Chronicles II 7:1-3)
This was the only time in Jewish history when the Jewish people did not fast on Yom Kippur. However, the Zohar says that there will be no fasting on Yom Kippur in the future world either. Yom Kippur will be one of the holidays that will remain after Moshiach comes, for the Torah says about it: “It will be for you an eternal law”, but the Zohar adds: “Purim was named after Yom Kippur because in the future, the day will be one of pleasure and instead of fasting, it will be joyous.”