Amitāśana (Amitasana) is one of the names of God Viṣṇu (Vishnu) as described in Viṇusahasranāmastotra (Vishnusahasranamastotra; Hymn of the Thousand Names of God Vishnu).

Mahābhārata (Kinjawadekar)(13.149.53)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)(13.127.53)