Numbers 11:21

שש 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).

וַיֹּ֘אמֶר֮ מֹשֶׁה֒ שֵׁשׁ־מֵא֥וֹת אֶ֙לֶף֙ רַגְלִ֔י הָעָ֕ם אֲשֶׁ֥ר אָנֹכִ֖י בְּקִרְבּ֑וֹ וְאַתָּ֣ה אָמַ֗רְתָּ בָּשָׂר֙ אֶתֵּ֣ן לָהֶ֔ם וְאָכְל֖וּ חֹ֥דֶשׁ יָמִֽים׃

And Moshe said, The people, among whom I am, are six hundred thousand footmen; and thou hast said, I will give them meat, that they may eat a whole month.