The Law Code of Yājñavalkya 3.1.13

3.1.13

ayam arthaḥ: caulakarmānantarakāle niyamenāgnyudakadānaṃ kāryam | anyatrāpi nāmakaraṇād ūrdhvaṃ akṛtacūḍe 'pīcchayā pretābhyudayakāmanayā dvayaṃ agnyudakadānātmakaṃ tūṣṇīṃ kāryaṃ na niyameneti vikalpaḥ | manunāpy atra viśeṣo darśitaḥ |

The meaning is this: immediately after the tonsure rite, the offering of fire and water is obligatorily to be performed. In other cases as well, after the naming ceremony, even when tonsure has not been performed, both consisting of the offering of fire and water may be performed silently at will, desiring the welfare of the deceased, not as an obligatory rule—this is an optional alternative. Manu too has indicated a specific rule here: