Christmas
From Urantia Wiki, the encyclopedia of The Urantia Book
Also: December twenty-fifth.
Christians celebrate actually on festival day of Mithras. Mithraists Three times a day they worshiped, with special weekly ceremonials on the day of the sun-god and with the most elaborate observance of all on the annual festival of Mithras, December twenty-fifth. 98:5.4
modern peoples continue reveling in the lavish distribution of Christmas gifts, and rich men endow great institutions of philanthropy and learning. This make tham feel great men. 69:5.13
The Maypole, the Christmas tree, and the superstitious practice of rapping on wood perpetuate certain of the ancient customs of tree worship and the later-day tree cults. 85:2.5
In the Urantia Book
> https://en.wikipedia.org/wiki/Mithraism
Where it appears
Christmas is linked in 3 paragraphs of the text.