Is Tantra part of the Sruti or Smriti? I am a bit confused about where to place Tantra. Please answer with references.
Sruti is divine revelation, while Smriti is a text that is authored by human beings. Vedas are revealed by Brahma at the beginning of creation. That's why it is a Sruti. Similarly, Tantras are revealed by Siva. Thus Tantras are also divine revelation and therefore should be part of Sruti.
Tantra is indeed placed under Sruti by Kulluka Bhatta. He is one of the famous commentators on Manu Smriti. In his commentary on Manu Smriti (Chapter II, Verse 1: Learn the Law always adhered to by people who are erudite, virtuous, and free from love and hate, the Law assented to by the heart.), he quoted Harita, who said that there are two types of Srutis - Veda and Tantra. Here is what he said -
श्रुतिश्च द्विबिधा वैदिकी तान्त्रिकीच (śrutiśca dbibidhā vaidikī tantrikīca)
So Tantra is part of Sruti.
- Manava Dharma Sastra with the commentaries of Medhatithi, Sarvajnanarayana, Kulluka, Raghavananda, Nandana and Ramachandra by Vishvanath Narayan Mandlik [in Sanskrit] (Page - 88, 104)
- Encyclopaedia of Tantra Volume I by Sadhu Santideva [in English] (Page - 8)
- Manu's code of Law - a critical Edition and translation of Manava Dharmashastra by Patrick Olivelle (Page 94)