Chabad.org — English translation + Rashi
Torah Temimah points to Toras Kohanim (Sifra), Vayikra Dibbura DeChovah, on 4:6.
Sefaria — Sifra / Toras Kohanim, Vayikra Dibbura DeChovah
English: “Seven times” — that he count seven times, and not one and seven.
Counting method for the seven — he counts seven distinct sprinklings; he does not use the Yom Kippur-style “one and seven” count.
He counts seven distinct sprinklings; he does not use the Yom Kippur-style “one and seven” count. The Sifra’s reading of “seven times” insists on a simple sequential count of seven applications rather than the special counting formula used on Yom Kippur. This keeps the blood service of the High Priest’s ordinary chatas distinct from the unique procedures of the Day of Atonement.