Brihat Parashara Hora Shastra
सवले लग्नपे पुत्रषष्ठपौ केन्द्रगौ मिथः । शंखो वा लग्नकर्मेशौ चरे बलिनि भाग्यपे ॥ १३॥
Shankh Yog. If Lagn‟s Lord is strong, while the Lords of Putr and Ari Bhava are in mutual Kendras, then what is known, as Shankh Yog, is produced. Alternatively, if Lagn‟s Lord along with Karm‟s Lord is in a Movable Rāśi, while Dharm‟s Lord is strong, Shankh Yog is obtained.
english translation
savale lagnape putraSaSThapau kendragau mithaH । zaMkho vA lagnakarmezau care balini bhAgyape ॥ 13॥
hk transliteration by Sanscript