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Ash Wednesday derives its name from the practice of placing ashes on the foreheads of adherents as a sign of mourning and repentance to God. The ashes used are typically gathered after the palms from the previous year's Palm Sunday are burned

According to the canonical gospels of Matthew, Mark and Luke, Jesus spent 40 days fasting in the desert before the beginning of his public ministry, during which he endured temptation by Satan. Ash Wednesday marks the beginning of this 40-day liturgical period of prayer and fasting.

At Masses and services of worship on this day, ashes are imposed on the foreheads of the faithful (or on the tonsure spots, in the case of some clergy). The priest, minister, or in some cases officiating layperson, marks the forehead of each participant with black ashes in the sign of the cross, which the worshipper traditionally retains until it wears off.

Turn away from sin and be faithful to the Gospel.
—Mark 1:15

Remember that thou art dust, and to dust thou shalt return.
—Genesis 3:19