The Shiva bhujanga Stotram of Shankaracharya alluded to in the Shankara Vijayam
In the Madhaviya Shankara Digvijayam, during the event of Shankaracharya visiting his mother in her deathbed, upon her beseeching him for the means for liberation, after her turning down his Nirguna Brahman upadesha, Shankara first prays to Lord Shiva. The Shankara Vijaya says that this prayer was in the form of a Bhujanga prayata meter. The commentary presents the Stotra in great length.
The stotra can be read here:
The Madhaviya Shankara Vijaya is admitted to be a composition of the 14th century. That means that the Shiva bhujanga Stotram has been existing from a period prior to this text. The Vijaya says in the beginning that this is a condensation of an ancient Vijaya.
It may be noted that there is a Vishnu bhujanga Stotra too attributed to Shankaracharya in popular parlance.
The image of the Shankara Vijaya is given below: