俱舍論記 4.122

4.122

「不善惡作至第二十一」者，此明不善惡作二十一俱生。不善惡作自力起故，所以不與貪等、忿等相應，唯與無明相應。

"Unwholesome remorse [...] is the twenty-first": this explains that twenty-one co-arise with unwholesome remorse. Because unwholesome remorse arises by its own power, it is not associated with greed and the like, or anger and the like, but is associated only with ignorance.