Chapter 2 · The Yoga of Knowledge · Krishna said
Bhagavad Gita 2.58 — Like a tortoise
यदा संहरते चायं कूर्मोऽङ्गानीव सर्वशः। इन्द्रियाणीन्द्रियार्थेभ्यस्तस्य प्रज्ञा प्रतिष्ठिता ॥
yadā saṃharate cāyaṃ kūrmo'ṅgānīva sarvaśaḥ | indriyāṇīndriyārthebhyastasya prajñā pratiṣṭhitā ||
Meaning
When a person can withdraw the senses from their objects completely, like a tortoise drawing in its limbs, that person's wisdom is steady.