Ekātmā (Ekatma) is one of the Sahasranāma (Sahasranama; Thousand Names) of God Viṣṇu (Vishnu).

Mahābhārata (Kinjawadekar)(13.149.116)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)(13.127.116)
   “]