Rashi on Numbers 11:21/רש"י על במדבר י״א:כ״א

1שש מאות אלף רגלי [THE PEOPLE AMONGST WHOM I AM ARE] SIX HUNDRED THOUSAND FOOTMEN — He was not particular to mention also the odd number — the remaining three thousand. But Rabbi Moses the Preacher explained that the number 600,000 is exact because only those who went forth from Egypt wept (since only they could have said, (v. 5) “We remember the fish which we did eat in Egypt”, and they who left Egypt are described, as here, by the term רגלי added to the number 600,000; cf. Exodus 12:37).