Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 13

Sanskrit:

निशाचरीत्थं व्यथितस्तना व्यसु-र्व्यादाय केशांश्चरणौ भुजावपि ।प्रसार्य गोष्ठे निजरूपमास्थितावज्राहतो वृत्र इवापतन्नृप ॥ १३ ॥

ITRANS:

niśā-carītthaṁ vyathita-stanā vyasurvyādāya keśāṁś caraṇau bhujāv apiprasārya goṣṭhe nija-rūpam āsthitāvajrāhato vṛtra ivāpatan nṛpa

Translation:

In this way the demon Pūtanā, very much aggrieved because her breast was being attacked by Kṛṣṇa, lost her life. O King Parīkṣit, opening her mouth wide and spreading her arms, legs and hair, she fell down in the pasturing ground in her original form as a Rākṣasī, as Vṛtrāsura had fallen when killed by the thunderbolt of Indra.

Purport:

Pūtanā was a great Rākṣasī who knew the art of covering her original form by mystic power, but when she was killed her mystic power could not hide her, and she appeared in her original form.