Brihat Parashara Hora Shastra
दशामध्ये फलं वाच्यं मध्यद्रेष्काणगे खगे । अन्ते फलं तृतीयस्थे व्यस्तं खेटे च वक्रगे ॥ ४॥
The Grah in the second Dreshkan makes its effects felt in the middle of the Dasha. The effects of the Grah in the third Dreshkan are experienced at the end of the Dasha. If the Grah is retrograde, these effects would be in the reverse order. The Dasha effects of Rahu and Ketu, who are always retrograde, will always be realized in the reverse order.
english translation
dazAmadhye phalaM vAcyaM madhyadreSkANage khage । ante phalaM tRtIyasthe vyastaM kheTe ca vakrage ॥ 4॥
hk transliteration by Sanscript