Skandapurana 5.161.57

5.161.57

kuśodakaṃ ca saṃprāśya kāyaśuddhimavāpnuyāt ..
vaiśākhe kiṃśukaiḥ pūjāṃ yathāvacca ghṛtāśanaiḥ .. 57 ..

And having sipped kuśa-water, one attains purification of the body. / In Vaiśākha, worship with kiṃśuka flowers and with offerings consumed by fire according to the rule;