bāhyābhyantaraviṣayākṣepī caturthaḥ [YS 2.51]

deśakālasaṃkhyābhir bāhyaviṣayaparidṛṣṭa ākṣiptaḥ. tathābhyantaraviṣayaparidṛṣṭa ākṣiptaḥ. ubhayathā dīrghasūkṣmaḥ. tatpūrvako bhūmijayāt krameṇobhayor gatyabhāvaś caturthaḥ prāṇāyāmaḥ. tṛtīyas tu viṣayānālocito gatyabhāvaḥ sakṛdārabdha eva deśakālasaṃkhyābhiḥ paridṛṣṭo dīrghasūkṣmaḥ. caturthas tu śvāsapraśvāsayor viṣayāvadhāraṇāt krameṇa bhūmijayād ubhayākṣepapūrvako gatyabhāvaś caturthaḥ prāṇāyāma ity ayaṃ viśeṣa iti.