Numbers 3:14

And the Lord spake with Mosheh in the wilderness of Sinai, saying:

AND THE ETERNAL SPOKE UNTO MOSES IN THE WILDERNESS OF SINAI. The reason for this statement is that since Scripture said above in the day that the Eternal spoke with Moses in Mount Sinai, it refers back and says [here] that the command for counting the Levites was not given in Mount Sinai; for only the choosing of the [four] children of Aaron [as priests] took place in Mount Sinai on the day that He commanded Moses about the making of the Tabernacle, but he was not given the command about the choosing of [all] the Levites [as ministers to the priests] at Mount Sinai, but in the wilderness of Sinai in the Tent of Meeting, just like the commandment mentioned [above] concerning [the counting of] the children of Israel [about which it is clearly stated that it was in the wilderness of Sinai, in the Tent of Meeting].
Now the tribe of Levi was not like all the other tribes, for [even though they were counted] from a month old and upward [unlike the other tribes who were counted only from the age of twenty years and over], they were still only twenty and two thousand, and from thirty years old and over they were all together [only] eight thousand [and five hundred and fourscore]., 4:48. Thus, their number from twenty years old and over does not reach even a half of the [number of the] smallest of [the other] tribes of Israel! And they did not as yet carry the ark, [that we should say] that its holiness took a toll of them! This is indeed astonishing, that His servants and His pious ones should not be blessed of the Eternal as were the rest of the people!
Therefore I am of the opinion that this is a confirmation of what our Rabbis have said, 6. See also Ramban on Exodus 5:4. that the tribe of Levi was not [subject to] the enslavement of Egyptian bondage and the rigorous work [that was imposed on the rest of the tribes]. Now since the children of Israel’s lives were made bitter by the Egyptians with hard work in order to diminish them, the Holy One, blessed be He, increased them [miraculously] to overcome the decree of the Egyptians, just as He said, And as they afflicted them, so they multiplied and so they grew,, Verse 12. and just as it is said also with reference to the decree that if it be a son, then ye shall kill him, Verse 16. — and the people multiplied, and waxed very mighty, Verse 20. — since the Holy One, blessed be He, said: “We shall see whose words shall stand, Mine or theirs. ” But the tribe of Levi [which was not subject to bondage] reproduced and increased in a normal way, and therefore they did not become as numerous as the other tribes. Perhaps also [their small numbers were] on account of the anger of the patriarch [Jacob] towards them, for the tribe of Shimon which now had a large population. decreased, so that at the time of their entry into the Land [they numbered only] twenty-two thousand [and two hundred — whereas most of the other tribes increased in the same period, or decreased relatively slightly]; similarly, Levi, the tribe of His pious ones, was not decreased in the plague [caused because of Peor, and yet at the time of entry into the Land they numbered only one thousand more, 26:62. than their present twenty-two thousand! Thus we see that it was the anger of the patriarch which affected the numbers of both Shimon and Levi.]