Yajur Veda · Krishna Yajur Veda (Yoga Upanishad group) · 142 mantras
Yoga Tattva Upanishad
Yoga-tattva-upaniṣad
Central theme: The four yogas — mantra, laya, hatha, raja — taught by Vishnu to Brahma
A minor (sāmānya-yoga) Upanishad of 142 mantras opening with Brahma's prostration before Vishnu and the question: "Teach me the science of yoga (yoga-tattvam) by which the jiva is freed from samsara." Vishnu replies with the classical four-fold yoga taxonomy: mantra-yoga (japa of an ishta-mantra for 12 years), laya-yoga (dissolution through the chitta's absorption in the object of meditation), hatha-yoga (the eight angas with detailed asana, eight kumbhakas and three bandhas), and raja-yoga (the highest, leading to kevala-kumbhaka and samadhi). Lists the obstacles (vighna), the four awakening stages (arambha, ghata, parichaya, nishpatti) and the eight siddhis with their grave dangers.
Yoga Tattva 19-20
मन्त्रो लयो हठो राजयोगोऽन्तर्भूमिकाः क्रमात् । एक एव चतुर्धाऽयं महायोग इति स्मृतः
Mantro layo haṭho rāja-yogo'ntar-bhūmikāḥ kramāt, eka eva caturdhā'yaṁ mahā-yoga iti smṛtaḥ
Mantra, laya, hatha and raja are the progressive inner stages — though four, this is remembered as the one Maha-Yoga.
Mantra is the doorway, laya the corridor, hatha the staircase, raja the throne room — and all four are one yoga.