大般涅槃經義記 1.28

1.28

次辯正義，蓋乃如來為化之辰，說之為時，化時眾多，簡別餘時，是故言一。此云何知？如彼《地經》大本之中云言「爾時佛在天中」，及其別傳改爾為一，爾時之言不可成上，改爾為一，寧不屬下？諸經之中大有此例，如下文中：我於一時在尸首林、我於一時在迦尸國、我於一時在王舍城、我於一時在恒河岸，如是非一。

Next, to discern the correct meaning: this is simply the occasion on which the Tathāgata engaged in teaching, which is spoken of as the 'time'; the occasions of teaching were numerous, and to distinguish it from other times, it therefore says 'at one [time].' How is this known? For example, in the larger version of that Daśabhūmika Sūtra it says: 'At that time the Buddha was among the devas'; when it came to a separate transmission, it changed 'at that' (er) to 'one' (yi). The words 'at that time' cannot be made to complete what is above; having changed 'that' to 'one,' how could it not belong to what follows? There are many instances of this throughout the sūtras, as in the text below: 'At one time I was in the Śmaśāna Forest,' 'At one time I was in the land of Kāśi,' 'At one time I was in Rājagṛha,' 'At one time I was on the bank of the Ganges'—cases like this are not just one.