Rashi on Exodus 30:21/רש"י על שמות ל׳:כ״א

1ולא ימתו THAT THEY DIE NOT — This statement is intended to declare subject to the death penalty anyone who ministers at the outer altar without having washed his hands and his feet, because from the first mention of “death” (v. 20) we can only infer that one is subject to death for entering the Sanctuary under these circumstances.