Bhagavad Gita 2.58
He who can withdraw his senses from the attraction of their objects, as the tortoise draws its limbs within its shell—take it that such a one has attained perfection.
यदा संहरते चायं कूर्मोऽङ्गानीव सर्वशः।
इन्द्रियाणीन्द्रियार्थेभ्यस्तस्य प्रज्ञा प्रतिष्ठिता॥yadā saṃharate cāyaṃ kūrmo'ṅgānīva sarvaśaḥ|
indriyāṇīndriyārthebhyastasya prajñā pratiṣṭhitā||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).