Iṣṭa(Ishta) is one of the names of God Viṣṇu(Vishnu) as mentioned in Viṣṇusahasranāmastotra (Vishnusahasranamastotra; the Hymn of Thousand Names of Vishnu).

Mahābhārata (Kinjawadekar)(13.149.47)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)(13.127.47)