Shiva sutras are core text of Kashmir Shaiva agamas.
What is the story behind Lord Vasugupta getting the revelation of Shiva sutras?
There are three theories regarding the revelation of the Siva-Sutra to VasuGupta.
"On the Mahavadeva mountain, the secret doctrines are inscribd on a piece of stone. Collecting the doctorines from there, teach them to those who deserve grace."
On waking up, Vasugupta went to the place and by a mere touch, the particular stone turned up and he found Siva-Sutras inscribed on it.
The Particular rock is still called Samkaropala. , and the rock is there but there is no trace of the Sutras.
Shiva Rock (Shankaropal), where fifteen hundred years ago, the Shiva Sutras were revealed to the Sage Vasugupta:
The story is told in the beginning of Kshemaraja's Shiva Sutra Vimarshini. The story is that Vasugupta is directed by Shiva in a dream to go to a certain slab, on which is written the Shiva Sutras:
There lived on Mahadevagiri the teacher, by name, Vasugupta, a great Maheshvara, who rejected the teachings of Nagabodhi and other teachers of inferior schools; for, by the grace of Shivashakti, he possessed great devotion to Maheshvara and always worshipped Shiva; and his heart was purified by following the paths of those who have mastered the Yoginis of Parameshvara. Once, in a dream, he was illuminated with right knowledge by the favour of Paramashiva, of Supreme Grace, who desired that the secret path should not be lost to the world of men, enveloped with the cognition of duality, and revealed to him: "On a huge slab on this mountain, there is a secret. Take it and make it known to those that are fit for Grace." On awaking, he searched for the stone, and found one that turned upside down as soon as he touched it. The dream proved true and thence he got these Shiva-sutras, which are the epitome of the Shivopanishad. Having obtained them, he published them to Bhatta Kallata and others of his disciples. He also embodied (the same teachings) in his Spandakarika.
Nagabodhi is a Buddhist philosopher, by the way. Also, other Kashmiri Shaivite works attribute the Spanda Karika to Vasudgupta's shishya Kalatta Bhatta rather than to Vasugupta himself.