Gita Mahatmya
Mahābhārata, Bhīṣma-parva 43.2
These verses glorify the Bhagavad-gītā. They come from other scriptures and are not verses of the Bhagavad-gītā itself. Each one carries its own source.
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Gītā-māhātmya
सर्वशास्त्रमयी गीता सर्वदेवमयो हरिः ।
सर्वतीर्थमयी गङ्गा सर्ववेदमयो मनुः ॥sarvaśāstramayī gītā sarvadevamayo hariḥ
sarvatīrthamayī gaṅgā sarvavedamayo manuḥThe Gītā holds all the scriptures, just as Lord Hari holds all the devatās, the Gaṅgā holds all the holy places, and Manu holds all the Vedas.
Source: Mahābhārata, Bhīṣma-parva 43.2