Pathamasikkhasutta 2.5

2.5

Yāni ca kho tāni sikkhāpadāni ādibrahmacariyakāni brahmacariyasāruppāni, tattha dhuvasīlo ca hoti ṭhitasīlo ca, samādāya sikkhati sikkhāpadesu.

But they’re constant and steady in their precepts regarding the training rules that are fundamental, befitting the spiritual path. They keep the rules they’ve undertaken.