This mudra has several names viz. Vyākhyāna (व्याख्यान), Vitarka (वितर्क), Sandarśana (सन्दर्शन) or, Ciṉ or Chin mudrā (छिन्मुद्रा).
Quoting from this PhD research thesis titled: 'The significance of the Mula beras in the Hindu temples of Tamilnadu: with special reference to Bharatanatyam and Hindu iconography'.
Vyākhyāna Mudrā (pages 108-109)
The thumb is held perpendicular to the palm and the index finger is
bent forward to touch the tip of the thumb. The remaining three
fingers are held close together vertically above the palm. It is known
variously as vyākhyāna, vitarka or ciṉ mudrā.
Rao remarks about it
that it is the “mudrā adopted when an explanation or exposition is
being given; hence it is also called vyākhyāna mudrā and sandarśana
mudrā.”‡
A commentary on the Ciṉ Mudrā's variation: 'jñana-mudrā':
Author Rao remarks‡, that when the same Ciṉ Mudrā is held near the heart it becomes Jñana-Mudrā, and not otherwise.
In the jñana-mudrā, the tips of the middle finger and of
the thumb are joined together and held near the heart, with
the palm of the hand turned towards the heart (see PI. V,
fig. 16).
(page 17)
‡
Gopinatha Rao, T. A. (1914). Elements of Hindu iconography: Volume I, Part I. India: Law Printing House.
Relevant portion quoted in the research paper may be read from this link of the book (pages 16-17) in the archive site.
Update:
then which scripture contains the chin mudra in detail?
After rigorous searching I was finally able to trace some scriptural information on Chin-mudrā (चिन-मुद्रा), also known by its another variant called jñana-mudrā‡(ज्ञान-मुद्रा):
This book named Mudrā Vimarśa (मुद्रा विमर्श) has information on almost all kinds/types of 'Hasta-Mudrās' used in tantras, and smarta sects.
In the sub-heading 68. Chin-mudrā (६८. चिन्मुद्रा) on page 29 of the book, the reader is directed to the jñana-mudrā sub-heading in the book.
The Jñana-Mudrā is found on page 31 of the said book subheading number 76 (७६)- ज्ञान.
As per the Book, the information is found in two canonical texts, and one non-canonical, viz.
-
- the Meru Tantra, and
-
- the Tantrasāra, attributed to Śrī Abhinavagupta of Trika sect,
-
- and the third reference is in an anthology series named - 'tantrokta-nitya-pūjā-paddhati-dhṛta kaulāvalī (तन्त्रोक्त-नित्य-पूजा-पद्धति-धृत कौलावली)'
Therefore, here's the scriptural references for Chin-Mudrā /Jñana-Mudrā (ज्ञान-मुद्रा१)
ज्ञानमुद्रा हृदिन्यस्तौ तर्जन्यगुष्ठको युतौ ।
वामहस्ताम्बुजं वा तु यदि मूर्द्धनि विन्यसेत्
॥
- Tantrasāra [तन्त्रसार (पृष्ट ४६४)]
तर्जन्यङ्गुष्ठको सक्तावग्रतो विन्यसेत् सुधी ।
वामहस्ताम्बुजं वामजानुमूर्द्धनि विन्यसेत् ॥
ज्ञानमुद्रा भवेदेषा
रामचन्द्रस्य प्रेयसी ।
- तन्त्रोक्त-नित्य-पूजा-पद्धति-धृत कौलावली
ज्ञानाल्यमुद्रया चैव पूजयेत् परमेश्वरीम् ।
अगुष्ठतर्जनीभ्यां तु ज्ञानमुद्रा
प्रकीर्तिता ॥
The footnote for the above, in the book says: -
[१]:
भगवान् राम एवं सरस्वती के पूजन क्रम में ज्ञान मुद्रा का प्रयोग होता है। सुखासन से बैठकर दाहिने हाथ की तर्जनीं एवं अङ्गुष्ठ के अग्र पर्यों को मिलाकर, हृदय पर स्थित करके, बाँये हाथ को वामजानु पर स्थापित करना ज्ञानमुद्रा है।
English Translation of the above footnote by Self
The Jñana-mudrā (Chin mudrā) is used in the worship of either god Śrí Rāma, or goddess Sarasvatí. Sitting in Sukhāsana, the tips of the middle finger and of the thumb, of the right hand, are joined together and held near the heart, while the left hand is kept rested on the left thigh. This is known as the Jñana-Mudrā.
