Yājñavalkya Śikṣā 150

150

pādādau ca padādau ca sam̐yyogāvagraheṣu ca
jaḥ śabda iti vijñeyo yo'nyaḥ sa ya iti smṛtaḥ

At the beginning of a quarter-verse, at the beginning of a word, and in consonant clusters and word-division pauses, / it is to be known as the sound ja; that which is otherwise is remembered as ya.