Ūrdhvaśāyī(Urdhvasayi) is one of the names of God Śiva (Siva), as mentioned in Śivasahasranāmastotra (Sivasahasranamastotra; The Hymn of the Thousand names of Siva).

[See Ūrdhvaretā]

Mahābhārata (Kinjawadekar)(13.17.46)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)(13.16.46)