Agnivesha / Tantra / Mahabharata

Drona said to Arjuna that even his guru Agnivesha was a disciple of Agastya for the Dhanurveda.
Source
Mahabharata Adiparva, Chapter 139, verse 9,
http://en.wikipedia.org/wiki/Agnivesh_tantra

http://ancientvoice.wikidot.com/mbh:agastya

http://www.sacred-texts.com/hin/m03/m03096.htm

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