Srimad-Bhagavatam: Canto 7 - Chapter 1 - Verse 20


व्यवसायेन तेऽनेन दुष्करेण मनस्विनाम् । तपोनिष्ठेन भवता जितोऽहं दितिनन्दन ॥ २० ॥


vyavasāyena te ’nenaduṣkareṇa manasvināmtapo-niṣṭhena bhavatājito ’haṁ diti-nandana


My dear son of Diti, with your great determination and austerity you have done what was impossible even for great saintly persons, and thus I have certainly been conquered by you.


In regard to the word jitaḥ, Śrīla Madhva Muni gives the following quotation from the Śabda-nirṇaya: parābhūtaṁ vaśa-sthaṁ ca jitabhid ucyate budhaiḥ. “If one comes under someone else’s control or is defeated by another, he is called jitaḥ.” Hiraṇyakaśipu’s austerity was so great and wonderful that even Lord Brahmā agreed to be conquered by him.