法界次第初門 1.108

1.108

外六塵界。此具如前，外六塵入中分別其相，乃更加以界之名義者，意同六根中立界名。

The six external sense-object dhātus. These are fully as explained previously in distinguishing their characteristics under the six external sense-object āyatanas; the intention in further appending the name and meaning of "dhātu" to them is the same as establishing the name of dhātu among the six faculties.