Mudgalapurana 3.15.36

3.15.36

māsau ca dvividhau proktau sauracāndrau vidhānataḥ |
saṅkrameṇa ravermāso jāyate ravijaḥ smṛtaḥ ||

And the months are said to be of two kinds according to rule: solar and lunar. / By the transit of the sun a month comes to be, remembered as born of the sun.