Yājñavalkya Śikṣā 177

177

hakāraṃ pañcamairyuktamantasthābhiśca sam̐yyutam
aurasaṃ taṃ vijānīyātkaṇṭhyamāhurasam̐yyutam

The speech sound h combined with the fifth [nasal] consonants and joined with semivowels, / one should know that to be chest-produced; they say it is throat-produced when uncombined.