SB 6.13.4
sri-suka uvaca
vrtra-vikrama-samvignah
sarve devah saharsibhih
tad-vadhayarthayann indram
naicchad bhito brhad-vadhat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Sri Sukadeva Gosvami answered: When all the great sages and demigods were disturbed by the extraordinary power of Vrtrasura, they had assembled to ask Indra to kill him. Indra, however, being afraid of killing a brahmana, declined their request.