The Law Code of Yājñavalkya 3.1.7

3.1.7

araṇye kāṣṭhavat tyaktvā ityasyāyamarthaḥ | yathāraṇye kāṣṭhaṃ tyaktvodāsīnās tadviṣaye bhavanti tathonadvivārṣikam api khātāyāṃ bhūmau parityajya tadviṣaye śrāddhādyaurdhvadehikeṣu udāsīnair bhavitavyam ity ācārādiprāptaśrāddhādyabhāvo 'nena dṛṣtāntena sūcyate | sa ca ghṛtenābhyajya yamagāthāḥ paṭhadbhir nidhātavyaḥ,

The meaning of “abandoning like a piece of wood in the forest” is this: Just as people become indifferent toward a piece of wood after abandoning it in the forest, so also, after abandoning [a child] under two years of age in a pit in the earth, they must remain indifferent toward it with regard to post-funeral rites such as śrāddha. By this analogy, the absence of śrāddha and similar rites that might be obtained through customary conduct is indicated. And that [child] should be laid down, having been anointed with ghee, by those reciting Yama-hymns,