Rashi on Exodus 25:19/רש"י על שמות כ״ה:י״ט

1ועשה כרוב אחד מקצה AND MAKE ONE CHERUB FROM ONE EXTREMITY — In order that you should not say that the preceding verse means two cherubim on each extremity, it was necessary to expressly state: “one cherub from the one extremity and one cherub from the other extremity”.

2מן הכפרת FROM THE COVER itself, תעשו את הכרבים SHALL YE MAKE THE CHERUBIM — This is the explanation of: (v. 18) “of beaten work shalt thou make them” — that thou shalt make them out of the cover itself and that thou shalt not make them by themselves and afterwards join them to the cover.