瑜伽論記 4.67

4.67

難云：第四有捨受，捨受名捨樂，四空有捨受，應亦名捨樂。故今解云：彼唯有心樂，此有身心樂，故但此名樂住，非四空。

An objection asks: the fourth [dhyāna] has the feeling of equanimity, and the feeling of equanimity is called the pleasure of equanimity; the four formless absorptions also have the feeling of equanimity, so they should also be called the pleasure of equanimity. Therefore, it is now explained: those only have mental pleasure, whereas this has pleasure of both body and mind; hence only this is called 'dwelling happily', not the four formless absorptions.