Some Shavaite scriptures declare Vishnu as supreme in some cases. Is there any mention of Shiva as supreme deity in Vaishnava scriptures?
The prajāpatis said: O greatest of all demigods, Mahādeva, Supersoul of all living entities and cause of their happiness and prosperity, we have come to the shelter of your lotus feet. Now please save us from this fiery poison, which is spreading all over the three worlds.
O lord, you are the cause of bondage and liberation of the entire universe because you are its ruler. Those who are advanced in spiritual consciousness surrender unto you, and therefore you are the cause of mitigating their distresses, and you are also the cause of their liberation. We therefore worship Your Lordship.
O lord, you are self-effulgent and supreme. You create this material world by your personal energy, and you assume the names Brahmā, Viṣṇu and Maheśvara when you act in creation, maintenance and annihilation.
You are the cause of all causes, the self-effulgent, inconceivable, impersonal Brahman, which is originally Parabrahman. You manifest various potencies in this cosmic manifestation.
O lord, you are the original source of Vedic literature. You are the original cause of material creation, the life force, the senses, the five elements, the three modes and the mahat-tattva. You are eternal time, determination and the two religious systems called truth [satya] and truthfulness [ṛta]. You are the shelter of the syllable om, which consists of three letters a-u-m.