SB 6.13 Summary
This chapter describes Indra's fear at having killed a brāhmaṇa (Vṛtrāsura), and it also describes how he fled and was saved by the grace of Lord Viṣṇu.
When all the demigods requested Indra to kill Vṛtrāsura, he refused because Vṛtrāsura was a brāhmaṇa. The demigods, however, encouraged Indra not to fear killing him because Indra was protected by the Nārāyaṇa-kavaca, or the Supreme Personality of Godhead Himself, Lord Nārāyaṇa. Even by a glimpse of the chanting of Nārāyaṇa's name, one becomes free from all the sinful reactions of killing a woman, a cow or a brāhmaṇa. The demigods advised Indra to perform an aśvamedha sacrifice, by which Nārāyaṇa would be pleased, for the performer of such a sacrifice is not implicated in sinful reactions even if he kills the entire universe.
Following this instruction from the demigods, King Indra fought Vṛtrāsura, but when Vṛtrāsura was killed, everyone was satisfied but King Indra, who knew Vṛtrāsura's position. This is the nature of a great personality. Even if a great personality acquires some opulence, he is always ashamed and regretful if he acquires it illegally. Indra could understand that he was certainly entangled by sinful reactions for killing a brāhmaṇa. Indeed, he could see sinful reaction personified following him, and thus he fled here and there in fear, thinking of how to rid himself of his sins. He went to Mānasa-sarovara, and there, under the protection of the goddess of fortune, he meditated for one thousand years. During this time, Nahuṣa reigned over the heavenly planets as the representative of Indra. Unfortunately, however, he was attracted by the beauty of Indra's wife, Śacīdevī, and because of his sinful desire he had to accept the body of a serpent in his next life. Indra later performed a great sacrifice with the help of exalted brāhmaṇas and saints. In this way he was released from the reactions of his sinful killing of a brāhmaṇa.