Here in Saundarya Lahiri, I found following verse of Adi Shankar
O! Mother! The celebrities, Brahma, Vishnu, Rudra and Indra are functioning as the four legs of your resting cot (the world). Lord Parama Siva is the white lustrous pseudo blanket (sky) covering Your body. Though He is pure white and crystalline in colour, He appears red due to the reflected red lustre of You from underneath. With this red hue, He gives the exciting impression as if he is the manifestation of Sringara rasa. 92
After reading it, surprisingly he believed in Param Shiva. Param Shiva is the supreme Brahman who is beyond trinities & the creator or the ultimate reality according to Shaiva Agamas and PurAns. I want to know what else he said about Param Shiva in any of his works?