瑜伽師地論略纂 8.141

8.141

論解二十一受，即如所列。　「或九種受」者，法師云：即初三位各為三位，故九也。此九攝一切受盡，更無別開餘門也。　又釋：九種者，樂等三受為三；四、樂身等三受；五、樂心等受；六、有味；七、無味；八、依耽嗜；九、依出離。合為九，開即十也。

The treatise explains twenty-one feelings, precisely as listed. Regarding "or nine kinds of feelings," the Dharma master says: each of the initial three categories is divided into three, hence nine. These nine subsume all feelings completely, without opening any other gates. Another explanation: regarding the nine kinds, the three feelings of pleasure and so forth are three; 4. the three feelings of physical pleasure and so forth; 5. feelings of mental pleasure and so forth; 6. with savoring; 7. without savoring; 8. based on craving; 9. based on renunciation. Combined they make nine; expanded they are ten.