yadā cha–When; ayam–this person; sarvaśaḥ–completely; saṁharate–withdraws; kūrmaḥ aṅgāni iva–like the limbs of a tortoise; indriyāṇi–the perceptual senses; indriya-arthebhyaḥ–from their objects (sound, touch, form, taste, and smell); (tadā)–then; tasya–his; prajñā–wisdom; pratiṣṭhitā–is firmly established. [58]

When one’s senses are controlled and totally withdrawn from their objects, like the limbs of the tortoise withdrawn in its shell, his wisdom is firmly established.