SB 6.13.4

śrī-śuka uvāca
vṛtra-vikrama-saṁvignāḥ
 sarve devāḥ saharṣibhiḥ
tad-vadhāyārthayann indraṁ
 naicchad bhīto bṛhad-vadhāt
Word for word: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; vṛtra — of Vṛtrāsura; vikrama — by the powerful activities; saṁvignāḥ — being full of anxieties; sarve — all; devāḥ — the demigods; saha ṛṣibhiḥ — with the great sages; tat-vadhāya — for the killing of him; ārthayan — requested; indram — Indra; na aicchat — declined; bhītaḥ — being afraid; bṛhat-vadhāt — due to killing a brāhmaṇa.
Translation: 
Śrī Śukadeva Gosvāmī answered: When all the great sages and demigods were disturbed by the extraordinary power of Vṛtrāsura, they had assembled to ask Indra to kill him. Indra, however, being afraid of killing a brāhmaṇa, declined their request.