After killing Vrtrasura, Indra went to the Manasa-sarovara Lake to become free from sinful reactions. When he left the lake, he performed an asvamedha-yajna and then returned to his own abode

Expressions researched:
"After killing Vṛtrāsura, Indra went to the Mānasa-sarovara Lake to become free from sinful reactions. When he left the lake, he performed an aśvamedha-yajña and then returned to his own abode"

Srimad-Bhagavatam

SB Canto 6

After killing Vṛtrāsura, Indra went to the Mānasa-sarovara Lake to become free from sinful reactions. When he left the lake, he performed an aśvamedha-yajña and then returned to his own abode.

SB 6.13.2, Translation and Purport

Thereafter, the demigods, the great saintly persons, the inhabitants of Pitṛloka and Bhūtaloka, the demons, the followers of the demigods, and also Lord Brahmā, Lord Śiva and the demigods subordinate to Indra all returned to their respective homes. While departing, however, no one spoke to Indra.

In this connection Śrīla Viśvanātha Cakravartī Ṭhākura comments:

brahmeśendrādaya iti; indrasya sva-dhiṣṇya-gamanaṁ nopapadyate

vṛtra-vadha-kṣaṇa eva brahma-hatyopadrava-prāpteḥ;

tasmāt tata ity anena mānasa-sarovarād āgatya

pravartitād aśvamedhāt parata iti vyākhyeyam.

Lord Brahmā, Lord Śiva and the other demigods returned to their respective abodes, but Indra did not, for he was disturbed at having killed Vṛtrāsura, who was actually a brāhmaṇa. After killing Vṛtrāsura, Indra went to the Mānasa-sarovara Lake to become free from sinful reactions. When he left the lake, he performed an aśvamedha-yajña and then returned to his own abode.