The Law Code of Yājñavalkya 1.10.211

1.10.211

ūrdhvaṃ tripakṣād yac chrāddhaṃ mṛte 'hany eva tad bhavet |
adhas tu kārayed dāhād āhitāgner dvijanmanaḥ ||
iti |

“The ancestral rite that occurs after three fortnights should take place on the day of death itself; / but prior to that, in the case of a twice-born who has established sacred fires, he should have it performed from [the day of] cremation.”