Yōga Sūtra 2.44

स्वाध्यायादिष्टदेवतासम्प्रयोगः।

svādhyāyādiṣṭadēvatāsamprayōgaḥ।

[स्वाध्यायात् इष्ट देवता सम्प्रयोगः।
svādhyāyāt = by self-study; iṣṭa = one's own preferred; dēvatā = deity; samprayōgaḥ = communion established with;]

By self-study communion with one's own preferred deity is established.