俱舍論頌疏論本 3.93

3.93

初無漏十三者，謂未知當知初無漏根，必成就十三根。言十三者，謂身、命、意、喜、樂、捨、苦、信等五根，及未知當知根。此加身苦者，若成未知當知根，必在欲界，故定有身苦也。

As for "the first undefiled, thirteen": it means that with the first undefiled faculty—the faculty of knowing what is not yet known—one necessarily possesses thirteen faculties. The thirteen are: body, life, mind, joy, pleasure, equanimity, pain, the five faculties beginning with faith, and the faculty of knowing what is not yet known. The reason body and pain are added here is that if one possesses the faculty of knowing what is not yet known, one is necessarily in the desire realm, and therefore definitely has body and pain.