(Ibid. 19) "And the L–rd said to Moses: Thus shall you say to the children of Israel" — In the language that I speak, thus shall you speak to the children of Israel — in the holy tongue. Wherever "koh" ("thus"), "kachah" ("in this wise"), "aniyah" ("answering"), and "amirah" ("Saying") are used, the holy tongue is understood.
Records God Telling Moses Thus Shall You Say to the Children
Mekhilta Tractate Bachodesh 9:19