Rashi on Numbers 23:10/רש"י על במדבר כ״ג:י׳

1מי מנה עפר יעקב וגו׳ WHO HATH COUNTED THE DUST OF JACOB [AND THE NUMBER OF THE FOURTH PART OF ISRAEL] — Understand this as the Targum does: [who has counted] the infants of the house of Jacob, who are compared to the dust of the earth (Genesis 13:16). The words מארבע משריתא in the Targum mean; [who can count … even one] of the four (רבע “a fourth”) banners (companies of the tribes). — Another explanation of עפר יעקב is: Countless are the commandments which they practise in connection with dust: (Deuteronomy 22:10) “Thou shalt not plough with an ox and an ass [together]”; (Leviticus 19:19): “Thou shalt not sow thy field with two kinds of seeds”. There are also the ashes of the red cow (Numbers 19:9 ff.), and the dust used in the ordeal to which a woman suspected of infidelity is subjected (Numbers 5:17), and others similar to these (Midrash Tanchuma, Balak 12).

2ומספר את רבע ישראל The word רבע implies their matings — the offspring which issues from their relations (cf. Nedarim 31a; and Rashi on Numbers 24:3).

3תמת נפשי מות ישרים LET ME DIE THE DEATH OF THE UPRIGHT amongst them.