瑜伽師地論略纂 4.24

4.24

三性業中，有覆無記業亦名無記業，非三善根、三不善根為因緣故。

Among karma of the three natures, veiled-unobscured karma is also called indeterminate karma, because it does not take the three wholesome roots or the three unwholesome roots as its causal condition.