In the fifth aliyah G-d commands Moshe to count the Levites. The criterion for counting the Levites is that they should be males from a month old upward. One of the verses in this aliyah says: "Moshe numbered them according to the word of G-d." Rashi says on that verse, that Moshe asked G-d how he could possibly go into tents to count the babies (who were included in the count starting at one month old), and G-d said "you do your part, and I'll do Mine"; Moshe went and stood outside each tent and a Divine voice came from the tent saying that such and such a number of infants are in this tent.