Manava Dharmashastra 9.174

9.174

krīṇīyād yas tv apatyārthaṃ mātāpitror yam antikāt
sa krītakaḥ sutas tasya sadṛśo 'sadṛśo 'pi vā //

If a man buys a (boy), whether equal or unequal (in good qualities), from his father and mother for the sake of having a son, that (child) is called a (son) bought (Kritaka).