Rashi on Numbers 23:18/רש"י על במדבר כ״ג:י״ח

1קום בלק RISE UP, BALAK — When he perceived that he was mocking at him, he set himself to annoy him, saying, “Stand on your feet; you have no right to remain seated, seeing that I am sent to you on a mission by the Omnipresent” (Midrash Tanchuma, Balak 13).

2בנו צפור SON OF ZIPPOR — This (the suffix ו to mark the construct) is often found as a Biblical Hebrew form, as in (Psalms 50:10), “beast of (חיתו) the forest”; (Genesis 1:24) “beast of (חיתו) the earth”; (Psalms 114:8), “to a spring of (מעינו) water”.