四分律比丘含注戒本 1.327

1.327

是中若自言所趣向處、所到處，若坐若臥。或不自言，並如憂婆私所說治。是中無定法，故言「不定」也。

Herein, whether he himself admits to where he went, where he reached, or whether he sat or lay down; or if he does not admit it himself, he is to be dealt with entirely according to what the upāsikā said. Because there is no fixed dharma herein, it is called 'indeterminate.'