俱舍論記 27.53

27.53

「後恩圓德至善趣三乘」者，於前三中，後恩圓德亦有四種，謂令永解脫三惡趣為三，令永解脫善趣生死為一，故名為四。或能安置善趣為一，復能安置三乘為三，故名為四。

On "Finally, the excellence of benevolence […] the good destinies and the three vehicles": Among the previous three, the final excellence of benevolence also has four kinds: namely, causing beings to be forever liberated from the three bad destinies constitutes three, and causing beings to be forever liberated from the saṃsāra of the good destinies constitutes one, hence they are called four. Alternatively, being able to establish beings in the good destinies constitutes one, and further being able to establish them in the three vehicles constitutes three, hence they are called four.