Brihat Parashara Hora Shastra
आत्मकारकमारभ्य कारकाख्यदशा क्रमात् । लग्नात् कारकपर्यन्तं संख्यामत्र दशां विदुः ॥ १७८॥
The system, under which the first Dasha is of the Atma Karak and the subsequent Dashas are of the remaining 7 Karakas in their order is known, as Karak Dasha. In this system the Dasha years are equal to the number of Rāśis, counted from Lagn up to the Karak concerned.
english translation
AtmakArakamArabhya kArakAkhyadazA kramAt । lagnAt kArakaparyantaM saMkhyAmatra dazAM viduH ॥ 178॥
hk transliteration by Sanscript