The Great Epic of the Bhārata dynasty 6.28.35

6.28.35

śrībhagavānuvāca |
asaṃśayaṃ mahābāho mano durnigrahaṃ calam |
abhyāsena tu kaunteya vairāgyeṇa ca gṛhyate || 35 ||

"The Holy One said, 'Without doubt, O thou of mighty arms the mind is difficult of subjugation and is restless. With practice, however, O son of Kunti, and with the abandonment of desire, it can be controlled. It is my belief that by him whose mind is not restrained, devotion is difficult of acquisition. But by one whose mind is restrained and who is assiduous, it is capable of acquisition with the aid of means.'