Cārāyaṇīya Śikṣā 2.35

2.35

vargavargacaturbhiḥ syuḥparasminpañcame yamāḥ
śavikāracchakārādirtrayasaṃnatu saṃjñitam

From the four [non-nasal consonants] of each class, twin transitional sounds arise before a following fifth [nasal consonant];
[and] the modification of ś [into] ch and so forth, but the triad is not designated [as a twin transitional sound].