觀無量壽佛經義疏 2.8

2.8

「如是」，稱理云如，離非曰是。決定可信，故云如是。二、明非自說。

'Thus': according with the principle is called 'thus' (ru); being free from error is called 'so' (shi). Because it is definitively trustworthy, it is said: 'Thus.' Second, clarifying that it was not his own speech.