SB 8.11.35

tapaḥ-sāramayaṁ tvāṣṭraṁ
 vṛtro yena vipāṭitaḥ
anye cāpi balopetāḥ
 sarvāstrair akṣata-tvacaḥ
Synonyms: 
tapaḥ — austerities; sāra-mayam — greatly powerful; tvāṣṭram — performed by Tvaṣṭā; vṛtraḥ — Vṛtrāsura; yena — by which; vipāṭitaḥ — was killed; anye — others; ca — also; api — indeed; bala-upetāḥ — very powerful persons; sarva — all kinds; astraiḥ — by weapons; akṣata — without being injured; tvacaḥ — their skin.
Translation: 
Vṛtrāsura was the essence of the austerities undergone by Tvaṣṭā, yet the thunderbolt killed him. Indeed, not only he but also many other stalwart heroes, whose very skin could not be injured even by all kinds of weapons, were killed by the same thunderbolt.