Just as fire manifests differently in pieces of wood of different sizes and qualities, the omnipotent Supreme Soul, having entered the bodies of higher and lower life forms created by His own potency, appears to assume the identity of each.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स्वमायया सृष्टमिदं सदसल्लक्षणं विभुः । प्रविष्ट ईयते तत्तत्स्वरूपोऽग्निरिवैधसि
svamāyayā sṛṣṭamidaṃ sadasallakṣaṇaṃ vibhuḥ | praviṣṭa īyate tattatsvarūpo'gnirivaidhasi
SB 11.7.47