Yōga Sūtra 3.43

कायाकाशयोः सम्बन्धसंयमाल्लघुतूलसमापत्तेश्चाकाशगमनम्।

kāyākāśayōḥ sambandhasaṁyamāllaghutūlasamāpattēścākāśagamanam।

[काय आकाशयोः सम्बन्ध संयमात् लघु तूल समापत्तेः च आकाश गमनम्।
kāya = body; ākāśayōḥ = sky; sambandha = relationship; saṁyamāt = summary of; laghu = light; tūla = like cotton fiber; samāpattēḥ = becomes; ca = and; ākāśa = in the sky; gamanam = travel;]

By samyama on the relationship between body and sky one can become as light as cotton fiber and can travel in the sky.