大般涅槃經義記 2.204

2.204

第三重結菩薩可知，「以是緣」下就前第二結答上問。以是如來住大涅槃，起種種化示現納妃生子因緣，故汝不應言羅睺羅實是佛子。「何以」下釋，久離煩惱，常不變故。

The third section re-summarizes the bodhisattvas and can be understood; from "for this reason" onward, it concludes in response to the preceding question with respect to the second section above. It is because the Tathāgata abides in Mahāparinirvāṇa and produces diverse transformations, displaying the circumstances of taking a consort and fathering a child, that you should not say that Rāhula is truly the Buddha's son. From "why is this?" onward, it explains that he has long departed from afflictions and is eternally unchanging.