Brihat Parashara Hora Shastra
वर्णदादपि भो विप्र लग्नवच्चिन्तयेत् फलम्। वर्णदात् सप्तमाद् भावत् कलत्रायुर्विचिन्तयेत्॥ १८॥
The Varnad Lagn be considered, as natal Lagn, while the 7th from Varnad will denote the longevity of the spouse,
english translation
varNadAdapi bho vipra lagnavaccintayet phalam। varNadAt saptamAd bhAvat kalatrAyurvicintayet॥ 18॥
hk transliteration by Sanscript