Skandapurana 5.8.83

5.8.83

.. śakra uvāca .. ..
vṛtreṇa nirjitāḥ sarve vayaṃ brāhmaṇasattama ..
sa vadhyo nahi śastrāṇāṃ sarveṣāṃ varapuṣṭitaḥ . 83 ..

Śakra said:
"We have all been conquered by Vṛtra, O best of brahmins. / Strengthened by a boon, he cannot be slain by any weapons. 83