瑜伽論記 4.335

4.335

問經言已下，第二問答因釋別經中，此說四無量三乘外道通修，唯依色四靜慮，行相寬故慈憶念第三定，悲憶念空處等而修習之，非入空處等定修四無量。若諸菩薩廣慧聲聞，依無色心了一切法修四無量，理雖不遮未見誠說。

From "Asking about what the sūtra says" below: in the second part, distinguishing the causes through questions and answers to explain the specific sūtra, it is said that the four immeasurables are cultivated in common by the three vehicles and by non-Buddhists, yet they rely only on the four dhyānas of the form realm. Because their mental aspects are expansive, benevolence is recollected and cultivated [even while based on] the third dhyāna, and compassion is recollected and cultivated [as directed toward] the sphere of infinite space, and so forth; one does not enter the concentration of the sphere of infinite space and so forth to cultivate the four immeasurables. If bodhisattvas and śrāvakas of vast wisdom cultivate the four immeasurables relying on the formless mind and comprehending all dharmas, although the principle does not prohibit it, we have not seen an explicit teaching to that effect.