SB 6.11.13
sa tam nrpendrahava-kamyaya ripum
vajrayudham bhratr-hanam vilokya
smarams ca tat-karma nr-samsam amhah
sokena mohena hasañ jagada
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O King, when the great hero Vrtrasura saw Indra, his enemy, the killer of his brother, standing before him with a thunderbolt in his hand, desiring to fight, Vrtrasura remembered how Indra had cruelly killed his brother. Thinking of Indra’s sinful activities, he became mad with lamentation and forgetfulness. Laughing sarcastically, he spoke as follows.