Hiranyakeshigrihyasutra 1.6.20.1

1.6.20.1

prāṅmukhaḥ pratyaṅmukhyā hastaṃ gṛhṇīyātpratyaṅmukhaḥ prāṅmukhyā vā \ yadi kāmayeta puṃso janayeyamityaṅguṣṭhaṃ gṛhṇīyāt \ yadi kāmayeta strīrityaṅgulīḥ \ yadi kāmayetobhayaṃ janayeyamityabhīva lomānyaṅguṣṭhaṃ sahāṅgulibhirgṛhṇīyāt \ sarasvati predamiva subhage vājinīvati tāṃ tvā viśvasya bhūtasya prajāyāmasyagrataḥ gṛhṇāmi te suprajāstvāya hastaṃ mayā patyā jaradaṣṭiryathāsat bhago aryamā savitā puraṃdhirmahyaṃ tvādurgārhapatyāya devāḥ \ iti \1\

Facing the east, while she faces the west, or facing the west, while she faces the east, he should seize her hand. If he desires to generate male children, let him seize her thumb; if he desires (to generate) female children, her other fingers; if he desires (to generate) both (male and female children), let him seize the thumb together with the other fingers, (so as to seize the hand) up to the hairs (on the hair-side of the hand).
(He should do so with the two Mantras),
'Sarasvatî! Promote this (our undertaking), O gracious one, rich in studs, thou whom we sing first of all that is.
'I seize thy hand that we may be blessed with offspring, that thou mayst live to old age with me, thy husband. Bhaga, Aryaman, Savitri, Purandhi, the gods have given thee to me that we may rule our house.'