“Sufficient unto the day is the evil thereof” is an aphorism which appears in the Sermon on the Mount in the Gospel of Matthew chapter 6 — Matthew 6:34.
The wording comes from the King James Version and the full verse reads: “Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof.”
It implies that we should not worry about the future, since each day contains an ample burden of evils and suffering.
By Evelyn Simak, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=14023625