Commentary for Berakhot 3:14

וממאי דהאי ובא השמש ביאת השמש והאי וטהר טהר יומא

How do we know that this [Scriptural reference], "and the sun would set" (lit.: "and the sun would come") refers to sunset, and "…and it would be pure" means that the day would be cleared?

Abraham Cohen Footnotes to the English Translation of Masechet Berakhot