俱舍論疏 14.149

14.149

「論曰至便發律儀故」，釋發戒時也。說三歸時未得戒，自稱近事便發戒也。

The commentary states: "The śāstra says: [...] because the saṃvara is immediately engendered", which explains the time when the precepts are engendered. At the time of reciting the three refuges, one has not yet obtained the precepts; upon personally proclaiming oneself an upāsaka, the precepts are immediately engendered.