金剛經纂要刊定記 4.339

4.339

若阿下。反釋。云若或作念言，我得阿羅漢果，便著我人等相，則與凡夫何所異哉？由此驗知，的無是念。

From "If an [arhat]" downward is the explanation in reverse. It means that if they were to form the thought, saying, "I have attained the fruit of an arhat," they would immediately grasp onto characteristics such as self and person; how then would they differ from an ordinary being? From this it is proven that they certainly have no such thought.