大毘盧遮那成佛經疏 10.78

10.78

次無能勝真言。是釋迦之眷屬，亦入寶處三昧如上而說真言。此是釋迦化身，隱其無量自在神力，而現此忿怒明王之形，謂降伏眾生而盡諸障也。

Next is the mantra of Aparājita. He is a member of Śākyamuni's retinue, and also enters the Ratnasambhava samādhi as above to speak the mantra. This is an emanation body of Śākyamuni, concealing his immeasurable autonomous supernatural power to manifest this form of a wrathful vidyārāja, meaning to subdue sentient beings and exhaust all obstacles.