Bhagavad Gita: Chapter 2, Verse 58

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

yadā saṁharate cāyaṁ kūrmo ’ṅgānīva sarvaśaḥ
indriyāṇīndriyārthebhyas tasya prajñā pratiṣṭhitā 2.58

One who is able to withdraw his senses from sense objects, as the tortoise draws its limbs within the shell, is firmly fixed in perfect consciousness.