One of the most popular forms of Shiva worshipped in South India is the sage Dakshinamurthi, whose name literally means "the South-facing form". Dakshinamurthi is the subject of the famous Dakshinamurthu Stotram, a hymn commonly attributed to Adi Shankarcharya (although this is disputed) which says this:
It is strange to see the very old disciples and the very young teacher, who sit under a banyan tree, with the teacher always observing silence, and the students getting all the doubts cleared.
The story as I understand it is that Shiva incarnated as a young sage named Dakahinamurthi, who sat under a banyan tree and silently imparted wisdom to the Sanatkumaras, four sages who are mind-born sons of Brahma.
My question is, what scriptures mention the sage Dakshinamurthi? I assume he's mentioned in various Shaiva Agamas, but it's very hard to date Agamic texts. And he is discussed in the Dakshinamurthi Upanishad, but that's believed by many to be a late text.
Is he discussed in the Puranas? All I've found is a passing reference in this excerpt from the Narada Purana, which says that a hymn to Shiva called the Shiva Nyasa was heard from the gods by Dakshinamurthi:
The deity of this (nyasa) is Ardhanarisha, the sage Dakshinamurti and the metre is Gayatri. The application of this mantra is for attaining everything.
I suppose it's akin to how the sage Narayana, an incarnation of Vishnu, was the seer of mantras to Vishnu like the Purusha Sukta of the Rig Veda, which I discuss here.
Also, this forum post claims that Dakshinamurthi is discussed in the "Suta Samhita" of the Skanda Purana, but the Motilal Banarsidass translation of the Skanda Purana is divided into Khandas, not Samhitas, so I'm not sure what part of the text constitutes the Suta Samhita.
Does anyone know any other scriptures which discuss Dakshinamurthi?