Yōga Sūtra 2.54

स्वविषयासम्प्रयोगे चित्तस्य स्वरूपानुकार इवेन्द्रियाणां प्रत्याहारः।

svaviṣayāsamprayōgē cittasya svarūpānukāra ivēndriyāṇāṁ pratyāhāraḥ।

[स्व विषय असम्प्रयोगे चित्तस्य स्वरूप अनुकार इव इन्द्रियाणां प्रत्याहारः।
sva viṣaya = its own topic i.e. perceived topics; asamprayōgē = not coming in contact with; cittasya = the consciousness; svarūpa = form; anukāra = as per; iva = is only; indriyāṇāṁ = senses; pratyāhāraḥ = is pratyāhāra or withdrawal;]

Ensuring perceived forms and its topics do not come in contact with consciousness is pratyāhāra or withdrawal of senses.