Asat is one of the names of God Śiva-Mahādeva (Siva-Mahadeva), as mentioned in Śivasahasranāmastotra (Sivasahasranamastotra; Hymn of the Thousand Names of Siva). In this stotra, God Śiva is addressed twice as both Sat and Asat , in two different śloka(s) (sloka; verse).
[See Sat]