[1] These tantras are found in the Nyingma Gyubum ("The Hundred Thousand Tantras of the Ancients"), volumes 9 and 10, folio numbers 143-159 of the edition edited by Dilgo Khyentse (Thimpu, Bhutan, 1973) of the gting skyes dgon pa byang manuscript.
[2] The full title of the Drathalgyur (Tibetan: སྒྲ་ཐལ་འགྱུར, Wylie: sgra thal 'gyur) is: sGra-thal-’gyur chen po’i rgyud (Skt., Shabda maha prasamga mula tantra).
The tantra states that all spiritual teachings are manifestations of the original primordial sound.
[1] The tantra describes numerous esoteric Dzogchen practices, such as semdzin ("holding the mind").
The Precious Treasury of the Way of Abiding that discusses a Dzogchen perspective of buddha-nature (sugata-garbha): Moreover, owing to their circumstances, among ordinary beings there is not a single one who is not a buddha.