楞伽阿跋多羅寶經註解 4.205

4.205

塵沙無油，喻如來雖為眾生眾苦所逼，乃至蠢動未盡涅槃，欲捨深心願樂亦不可得，以大悲心具足成就眾生故也。

Dust and sand having no oil illustrates that although the Tathāgata is oppressed by the manifold sufferings of sentient beings, until all creeping and wriggling things have completely entered nirvāṇa, wishing him to abandon the delight of his deeply felt vows is likewise impossible, because he fully accomplishes sentient beings with a mind of great compassion.