Devibhagavatapurana 4.12.19

4.12.19

vyāsa uvāca |
gatā nidrā surendrasya dehe'kṣemamabhūnnṛpa |
smṛtvā kāvyasya vṛttāntaṃ mantrārthamatidāruṇam ||

Vyâsa said:-- O king! Though the deep sleep that overtook Indra had now left him, yet he became very unhappy, remembering the severe asceticism of S’ukra’s tapasyâ and his receiving mantras.