法華玄論 9.128

9.128

答：通義亦然，但化身從報身起，故非正酬因義。報身正酬因義，故名報也。又化身既為化二乘，此身既劣非是勝報，故不名報身也。

Answer: In a general sense that is also true, but the nirmāṇakāya arises from the saṃbhogakāya, so it does not possess the primary meaning of recompensing causes. The saṃbhogakāya has the primary meaning of recompensing causes, and is therefore named "reward". Furthermore, since the nirmāṇakāya is for converting the two vehicles, this body is inferior and is not an exalted reward; therefore it is not named the reward body.