Māṇḍūkī Śikṣā 105

105

rephoṣmaṇāṃ saṃyoge svarabhaktirakramaścaiva
tatrodāharaṇānāṃ pradarśanam varṣo barhiśca

In the conjunction of an r-sound and a spirant, there is a vowel glide and absence of doubling; / there the presentation of examples is *varṣaḥ* and *barhiḥ*.