Manava Dharmashastra 9.147

9.147

yā niyuktānyataḥ putraṃ devarād vāpy avāpnuyāt
taṃ kāmajam arikthīyaṃ pracakṣate //

If a woman (duly) appointed bears a son to her brother-in-law or to another (Sapinda), that (son, if he is) begotten through desire, they declare (to be) incapable of inheriting and to be produced in vain.