Yōga Sūtra 3.42

श्रोत्राकाशयोः सम्बन्धसंयमाद्दिव्यं श्रोत्रम्।

śrōtrākāśayōḥ sambandhasaṁyamāddivyaṁ śrōtram।

[श्रोत्र आकाशयोः सम्बन्ध संयमात् दिव्यं श्रोत्रम्।
śrōtra = hearing; ākāśayōḥ = sky; sambandha = relationship between; saṁyamāt = integration of; divyaṁ = gains divine; śrōtram = haering;]

By samyama on the relationship between sky and hearing, one gains divine hearing.