大乘起信論義記 3.228

3.228

辨因中，如是依正二報無障礙不思議事，皆因十度深行之熏及本覺不思議熏二因所成，樂相圓備故名報身。故云如是功德乃至說為報身。

In distinguishing the causes: such unobstructed, inconceivable phenomena of both primary and dependent retributions are entirely accomplished by two causes: the perfuming of the profound practices of the ten perfections and the inconceivable perfuming of innate enlightenment. Because the marks of bliss are completely perfected, it is named the reward body. Therefore it says, 'Such merits' down to 'is called the reward body.'