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यदा संहरते चायं कूर्मोऽङ्गानीव सर्वशः ।
इन्द्रियाणीन्द्रियार्थेभ्यस्तस्य प्रज्ञा प्रतिष्ठिता ॥२- ५८॥

yadaa saMharate chaayaM koormo'~Ngaaniiwa sarwashaH ।

indriyaaNiindriyaarthebhyastasya pradnyaa pratiShThitaa ॥२- ५८॥

Source: Automatic ITRANS Transliteration

And as when a tortoise withdraws all its limbs,
[One who withdraws] senses from sense objects, that one's insight is stabilized.

Source: Milind S. Pandit

When one can completely withdraw (or restrain) the senses from the sense objects as a tortoise withdraws its limbs (into the shell), then the Prajna of such a person is considered steady.

Source: The Bhagavad-Gita: The Sacred Song

One who is able to withdraw his senses from sense objects, as the tortoise draws its limbs within the shell, is to be understood as truly situated in knowledge.

Source: Bhagavad Gita As It Is