Bhagwad Gita
Chapter 2, Verse 58
यदा संहरते चायं कूर्मोऽङ्गानीव सर्वशः।
इन्द्रियाणीन्द्रियार्थेभ्यस्तस्य प्रज्ञा प्रतिष्ठिता।।2.58।।
One who is able to withdraw his senses from sense objects, as the tortoise draws his limbs within the shell, is to be understood as truly situated in knowledge.