Agnipurana 331.3

331.3

pādasyādyantu vakraṃ syāt śanau na prathamāsmṛtau
bālyamuścaturthādvarṇāt pathyā varṇaṃ yujoyataḥ

The beginning of the quarter is Vakra; śa and nau are not taught as the first; / from the fourth syllable is the Vālyam; Pathyā joins syllables from that [pattern];