俱舍論疏 24.119

24.119

論「如是盡智至得無學名」，釋無學也。為得別果所應學者，名為有學。諸阿羅漢雖為得利根及諸功德，有所應學。然無為得別果所應學故，名為無學。捨其鈍果得利果者，即是得前所捨之果，非是別異得果，不名為學。

The Śāstra says: "Such knowledge of destruction […] obtains the name 'non-trainee'." This explains the non-trainee. One who should train in order to attain a further fruit is called a trainee. Although all arhats have things they should train in to attain sharp faculties and various virtues, because they have nothing they should train in to attain a further fruit, they are called non-trainees. Relinquishing a dull fruit to attain a sharp fruit is simply attaining the fruit previously relinquished; it is not the attainment of a distinct fruit, so it is not called 'training'.