首楞嚴義疏注經 6.39

6.39

欲身自在，遊行十方，現二天身說法教化，即夜摩、覩史天也。名自在者，慈恩云：「得異熟果，隨意所念，勝下二天。下二天果依樹而得，今隨欲得，名為自在。」

Wishing for the body to have mastery and roam through the ten directions, [the Bodhisattva] appears in the body of two devas to expound the Dharma and transform them: namely, the Yāma and Tuṣita devas. As for being named 'mastery' (īśvara), Ci'en says: 'Having attained the fruit of maturation, [manifesting objects] according to whatever they mentally intend, they surpass the lower two heavens. The fruits of the lower two heavens are obtained dependent on trees; now, being obtained according to desire, it is named mastery.'