瑜伽論記 9.320

9.320

解云：佛身雖無三界染種，欲令愛恚好惡色眾生故，變好為惡，其事云何，以隨悲願心上即有影像好惡相現，似有好實，實是無漏，由此為緣令彼眾生好色滅惡生。

The explanation says: Although in the Buddha's body there are no defiled seeds of the three realms, because he wishes to [help] sentient beings who love or despise good or bad forms, he transforms good into bad. How is this so? In accordance with the mind of compassionate vow, images of good and bad appearances directly appear thereon; there appears to be good reality, but in reality it is taintless. With this serving as a condition, the good forms of those sentient beings are caused to cease and bad forms arise.