大般涅槃經義記 1.28

1.28

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.