Revelation 7:4-8 (see also John 15:16, 19)
And I heard the number of those who were sealed, one hundred and forty-four thousand sealed from every tribe of the sons of Israel: from the tribe of Judah, twelve thousand were sealed, from the tribe of Reuben twelve thousand, from the tribe of Gad twelve thousand, from the tribe of Asher twelve thousand, from the tribe of Naphtali twelve thousand, from the tribe of Manasseh twelve thousand, from the tribe of Simeon twelve thousand, from the tribe of Levi twelve thousand, from the tribe of Issachar twelve thousand, from the tribe of Zebulun twelve thousand, from the tribe of Joseph twelve thousand, from the tribe of Benjamin, twelve thousand were sealed.
Calvinist, John MacArthur, comments: “That there were 12,000 sealed from every tribe of the sons of Israel speaks of God’s elective purpose. Mere random human choice would not come up with such an even division.” (The MacArthur New Testament Commentary: Revelation 1-11, p.220, emphasis mine)
Gary Cohen and Salem Kirban comment: “God in His sovereign good pleasure has elected to save this number during the early stages of the Tribulation Period, before the Trumpet Judgments fall, so that they can testify for Him to the many Jews and gentiles who are to be persecuted by the Antichrist. Is 12,000 a literal number? Perhaps yes. Perhaps, however, the rounded number 12,000 represents the elect found in each tribe whatever that number turns out to be. Will these be the only Jews saved during the Tribulation? No. These are saved during this period; many more shall be saved at Christ’s coming at its close (Zech. 12:10; Rom 11:26).” (Revelation Visualized, p.128, emphasis mine)