Darshana Upanishad 248

248

yāvadvā śakyate tāvaddhārayejjapatatparaḥ |
pūritaṃ recayet paścānmakāreṇānilaṃ budhaḥ || 5 ||

Or one should hold it as long as one is able, intent upon the recitation. / Afterwards, the wise one should exhale the inhaled air with the syllable 'M', || 5