Srimad Bhagavatam Canto 04, Chapter 06, Text 38

SB 4.6.38

krtvorau daksine savyam
pada-padmam ca januni
bahum prakosthe ’ksa-malam
asinam tarka-mudraya
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
His left leg was placed on his right thigh, and his left hand was placed on his left thigh. [This sitting posture is called virasana.] In his right hand he held rudraksa beads, and his finger was in the mode of argument.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The sitting posture described herein is called virasana according to the system of astanga-yoga performances. In the performance of yoga there are eight divisions, such as yama and niyama controlling, following the rules and regulations, then practicing the sitting postures, etc. Besides virasana there are other sitting postures, such as padmasana and siddhasana. Practice of these asanas without elevating oneself to the position of realizing the Supersoul, Visnu, is not the perfectional stage of yoga. Lord Siva is called yogisvara, the master of all yogis, and Krsna is called yogesvara. Yogisvara indicates that no one can surpass the yoga practice of Lord Siva, and yogesvara indicates that no one can surpass the yogic perfection of Krsna. Another significant word is tarka-mudra. This indicates that the fingers are opened and the second finger is raised, along with the arm, to impress the audience with some subject matter. This is actually a symbolic representation.
Srimad Bhagavatam Canto 04, Chapter 06, Text 37
Srimad Bhagavatam Canto 04, Chapter 06, Text 39