Grammatical Sūtra: नित्यं छन्दसि nityaṃ chandasi 
Individual Word Components: nityam chandasi
Sūtra with anuvṛtti words: nityam chandasi pratyayaḥ (3.1.1), paraḥ (3.1.2), ca (3.1.2), ādyudāttaḥ (3.1.3), ca (3.1.3), ṅyāpprātipadikāt (4.1.1), striyām (4.1.3), anupasarjanāt (4.1.14), ṅīṣ (4.1.40), bahvādibhyaḥ (4.1.45)
Type of Rule: vidhi
Preceding adhikāra rule:4.1.14 (1anupasarjanāt)
Description:
The affix ((ṅīṣ)) is always employed in the Vedic literature, in forming the feminine of the words ((bahu)) and the rest. Source: Aṣṭādhyāyī 2.0
In the domain of Chándas [the affix 3.1.1 ṄīṢ 40] is necessarily (nítya-m) introduced [after 3.1.2 the class of nominal stems 1 beginning with bahú- 45 to derive feminine 3 nominal stems 1]. Source: From Aṣṭādhyāyī of Pāṇini In Roman Transliteration translated by Sumitra M. Katre, Copyright © 1987. Courtesy of the University of Texas Press.