俱舍論記 25.32

25.32

「或修斷惑至定無退義」者，又解修惑非審慮生，聖容退起；見惑由審慮生，故聖不退。上來說一切有部明初得果不退義也。

Regarding 'Or, defilements abandoned by cultivation… there is definitely no meaning of falling away': this is another explanation: defilements of cultivation are not generated through deliberation, so noble ones can fall away and have them arise; defilements of seeing are generated through deliberation, so noble ones do not fall away from them. The above is the Sarvāstivāda's clarification of the meaning that the initially obtained fruit is not fallen away from.