kāryaṁ guṇāvatāratvenaikyād rudrasya vaiṣṇavaiḥ
kāryaṁ guṇāvatāratvenaikyād rudrasya vaiṣṇavaiḥ |
vaiṣṇavāgryatayā śreṣṭhyāt sadācārāc ca tad-vratam ||
(Hari-bhakti-vilāsa: 14.195)
“This vrata [i.e., Śiva Rātri] is to be performed by Vaiṣṇavas (1) because of Rudra’s oneness [with Bhagavān Viṣṇu] on account of [his] being a guṇāvatāra [of Bhagavān Viṣṇu], (2) because of [his] superiority [to other devatās] on account of [his] being the foremost of Vaiṣṇavas, and (3) because of proper conduct [i.e., because it is considered proper conduct to do so since it is a great fault to not].”