注維摩詰經 9.278

9.278

生曰：夫有人佛者，要從六入積而或出也。既無有積，夫有人佛乎？五是四大所造，故就六以明之焉。

[Dao]sheng says: If there is a human Buddha, he must appear through the accumulation of the six sense bases. Since there is no accumulation, is there a human Buddha? The [first] five are created by the four great elements, so he clarifies it with respect to the six.