Parashas Acharei Mos · Passuk 17:13
Chabad.org — English translation + Rashi
Torah Temima points to Prisha / Levush (Yoreh De’ah 28).
English: The vocalization “be’afar” (with a segol) teaches that the dust must be prepared in advance for the purpose of covering.
Intentional preparation of the dust
One should set aside the covering material beforehand rather than scooping it up incidentally.