Bereshit 11:1

שפה אחת ONE LANGUAGE — The Holy Tongue (Hebrew) (Midrash Tanchuma, Noach 19). ודברים אחדים AND ONE SPEECH — They came with one plan, saying: “He has no right to select the heavenly regions exclusively for Himself; let us ascend to the skies and make war upon Him”. Another explanation (of דברים אחדים which is taken to mean “words referring to “One”): words regarding the Sole Being (God) in the Universe. Another explanation of ודברים אחדים is: they spoke דברים חדים “sharp” words; they said, “Once in every one thousand six hundred and fifty six years (the period that elapsed from the Creation to the Flood) there is a heaven-shaking, just as there was in the days of the Flood. Come. then, and let us make supports for it” (Genesis Rabbah 38:6).

וַיְהִ֥י כׇל־הָאָ֖רֶץ שָׂפָ֣ה אֶחָ֑ת וּדְבָרִ֖ים אֲחָדִֽים׃

And the whole earth was of one language, and of one speech.