俱舍論記 25.39

25.39

「經言不動至從此退故」者，經部引證。又經說言不為惑動，心解脫惑身中證得滅，我定說無因緣從此退故。不動即是阿羅漢果，故知不退。

Regarding 'A sūtra says: "Unshakeable… falling away from this"': the Sautrāntikas cite proof. Furthermore, a sūtra says: 'Unshaken by defilements, the liberation of mind from defilements is realized cessation within the body; I definitely say there are no causes or conditions for falling away from this.' Unshakeable is precisely the fruit of arhatship, and so it is known that there is no falling away.