SB 8.11.32

na tasya hi tvacam api vajra ūrjito
 bibheda yaḥ sura-patinaujaseritaḥ
tad adbhutaṁ param ativīrya-vṛtra-bhit
 tiraskṛto namuci-śirodhara-tvacā
Synonyms: 
na — not; tasya — of him (Namuci); hi — indeed; tvacam api — even the skin; vajraḥ — the thunderbolt; ūrjitaḥ — very powerful; bibheda — could pierce; yaḥ — the weapon which; sura-patinā — by the king of the demigods; ojasā — very forcefully; īritaḥ — had been released; tat — therefore; adbhutam param — it was extraordinarily wonderful; ativīrya-vṛtra-bhit — so powerful that it could pierce the body of the very powerful Vṛtrāsura; tiraskṛtaḥ — (now in the future) which had been repelled; namuci-śirodhara-tvacā — by the skin of Namuci’s neck.
Translation: 
Although King Indra hurled his thunderbolt at Namuci with great force, it could not even pierce his skin. It is very wonderful that the famed thunderbolt that had pierced the body of Vṛtrāsura could not even slightly injure the skin of Namuci’s neck.