俱舍論記 2.101

2.101

「至意位時至無改易故」者，通。六識至過去意位時，不失六識界。現、未未至過去意位，亦非越意相。「若異此者」下，反難外人顯違宗過。又若未、現六識無意界相，過去意界亦應不立，此宗說相三世無改。

Regarding "When they reach the position of the mind... because there is no alteration": this resolves [the objection]. When the six consciousnesses reach the past position of the mind, they do not lose their character as consciousness-elements; in the present and future, not having reached the past position of the mind, they also do not depart from the characteristic of the mind-element. Below, "If it were otherwise" challenges the opponent in reverse to reveal the fault of contradicting their own tenets. Furthermore, if the future and present six consciousnesses lacked the characteristics of the mind-element, the past mind-element also could not be established; this school maintains that characteristics do not change throughout the three times.