Skandapurana 5.272.9

5.272.9

ṣaṇmāsāśca dinārdhaṃ ca prathamaṃ śuklapūrvakam..
saurasāvanacaṃdrārkṣairmānairebhiścaturvidhaiḥ .. 9 ..

and six months, and half a day, the first [half] beginning with the bright fortnight. / By these four types of measure—solar, civil, lunar, and sidereal—