The Law Code of Yājñavalkya 1.3.117

1.3.117

loke ānantyaṃ vaṃśasyāvicchedaḥ divaḥ prāptiś ca dārasaṃgrahasya prayojanam | katham ity āha | putrapautraprapautrakaiḥ lokānantyam agnihotrādibhiś ca svargaprāptir ity anvayaḥ | yasmāt strībhya etad dvayaṃ bhavati tasmāt striyaḥ sevyā upabhogyāḥ prajārtham | rakṣitavyāś ca dharmartham | tathā ca apastambena dharmaprajāsaṃpattiḥ prayojanaṃ dārasaṃgrahasyoktaṃ dharmaprajāsaṃpanneṣu dāreṣu nānyāṃ kurvīta (ĀpDh 2.11.12) iti vadatā | ratiphalaṃ tu laukikam eva || 1.78 ||

Infinity of worlds—meaning the non-interruption of one's lineage—and attainment of heaven are the purpose of taking a wife. How? He explains: infinity of worlds through sons, grandsons, and great-grandsons, and attainment of heaven through the Agnihotra and other [rites]—this is the syntactical connection. Because these two arise from women, therefore women are to be served, that is, enjoyed for the sake of offspring; and they are to be protected for the sake of duty. And likewise, the attainment of duty and offspring is stated by Āpastamba as the purpose of taking a wife, when he says: "When one has a wife endowed with duty and offspring, he should not take another" (ĀpDh 2.11.12). The fruit of sexual pleasure, however, is purely worldly.