Brihat Parashara Hora Shastra
पञ्चमं चार्गलास्थानं नवमं तद्विरोधकृत् । तमोग्रहभवा सा च व्यत्ययाज् ज्ञायते द्विज ॥ ६॥
The 5th is also an Argala place, while the Grah in the 9th will counteract such Argala. As Rahu and Ketu have retrograde motions, the Argalas and obstructions be also counted accordingly in a reverse manner.
english translation
paJcamaM cArgalAsthAnaM navamaM tadvirodhakRt । tamograhabhavA sA ca vyatyayAj jJAyate dvija ॥ 6॥
hk transliteration by Sanscript