Where lord Shiva is mentioned as guru (teacher) of saptarshis, Sanatakumara and universal teacher?
I was wondering this question but please mention smritis along with shrutis.
यत्र यत्र स्थितो देवः सर्वव्यापी महेश्वरः ।
यो गुरुः सर्वदेवानां यकाराय नमो नमः ॥६॥
Yatra Yatra Sthito Devah Sarva-Vyaapii Mahe[a-Ii]shvarah |
Yo Guruh Sarva-Devaanaam Yakaaraaya Namo Namah ||6||
6.1: (Salutations to Him) Who is Present Everywhere Where ever the Devas Abide, 6.2: Who is the Guru of All Devas, Salutations to that Shiva, Who is represented by syllable "Ya", The sixth syllable of the Sadakshara mantra "Om-Na-Ma-Shi-Va-Ya".
This the 6th verse of the Shivashadakshra Stotram, which is found in Rudra Yamala Tantram (a Shakta Tantra). Lord Shiva himself is the composer of the Stotram.
Here, he is described as "Yo Guruh Sarva Devanam" so kind of an universal teacher.
Lord Shiva's Dakshinamurty aspect is actually regarded as the "Universal Guru"- the Guru of all. In this Stotram composed by Adi Shankara (so neither Sruti nor Smriti though) we find:
सकलमुनिजनानां ज्ञानदातारमारात् ।
जननमरणदुःखच्छेद दक्षं नमामि ॥२॥
Sakala-Muni-Janaanaam Jnyaana-Daataaram-Aaraat |
Janana-Maranna-Duhkhac-Cheda Dakssam Namaami ||2||
2.1: Sitting on the ground near the Banyan Tree, ... 2.2: ... were all Munis (Sages), who were (sitting) near to the bestower of Knowledge, ... 2.3: ... who were (sitting) near to the Guru of the Three Worlds, the Lord Himself, personified as Dakshinamurthy Deva, ... 2.4: ... who were (sitting) near to the one, expert in severing the sorrows resulting from the cycles of Births and Deaths; I bow to that Dakshinamurthy.
And, the following verse which is widely used by those persons who are yet to have personal Gurus. This is widely chanted at the beginning of recitals or Pujas.
निधये सर्वविद्यानां भिषजे भवरोगिणाम् ।
गुरवे सर्वलोकानां दक्षिणामूर्तये नमः ॥४॥
Nidhaye Sarva-Vidyaanaam Bhissaje Bhava-Roginnaam |
Gurave Sarva-Lokaanaam Dakssinnaamuurtaye Namah ||4||
4.1: (Salutations to Sri Dakshinamurthy) Who is a receptacle to all Knowledge, Who is a Medicine to all the diseases of Worldly bondage, 4.2: Who is a Guru to all the Worlds; Salutations to Sri Dakshinamurthy.