Surya Siddhanta
अधिमासोनरात्र्यार्क्षचान्द्रसावनवासराः। एते सहस्रगुणिताः कल्पे स्युर् भगणादयः ॥
The revolutions of the planets, the additive months, the subtractive days, the sidereal days, the lunar days and the terrestrial days (mentioned above) separately multiplied by 1000 make the revolutions, the additive months &c., in a Kalpa, (because a Kalpa consists of 1000 great yugas.)
english translation
adhimAsonarAtryArkSacAndrasAvanavAsarAH। ete sahasraguNitAH kalpe syur bhagaNAdayaH ॥
hk transliteration by Sanscript