Mark 13:14

So when you see the abomination of desolation standing where it should not be (let the reader understand), then let those who are in Judea flee to the mountains.

Note See Daniel 9:27, Daniel 11:31, and Daniel 12:11; BYZ and TR include spoken of by Daniel the prophet.

Note Or where he should not be

BSB · Berean Standard Bible
But when ye shall see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not, (let him that readeth understand,) then let them that be in Judæa flee to the mountains:
KJV · King James Version
“But when you see the abomination of desolation, spoken of by Daniel the prophet, standing where it ought not” (let the reader understand), “then let those who are in Judea flee to the mountains,
WEB · World English Bible
But when ye see the abomination of desolation standing where he ought not (let him that readeth understand), then let them that are in Judæa flee unto the mountains:
ASV · American Standard Version

Related passages

From the Treasury of Scripture Knowledge, grouped by the word they explain.

the abomination
Daniel 8:13; Daniel 9:27; Daniel 12:11; Matthew 24:15–28; Luke 21:20–22
where
Lamentations 1:10; Ezekiel 44:9
let him
Matthew 13:51; Acts 8:30, 31; 1 Corinthians 14:7, 8, 20; Revelation 1:3; Revelation 13:18
then
Luke 21:21–24