Cārāyaṇīya Śikṣā 2.37

2.37

vargyāntyācchoṣasaiḥ sārdhamantasthairvāpi saṃyutam
dṛṣṭvā yamā nivartante ādeśagamivābdagaḥ

Seeing [a stop consonant] conjoined with class-finals, with ś, ṣ, s, or with semivowels,
twin transitional sounds turn back, like a traveler returning home from an assigned mission.