Garudapurana 1.50.84

1.50.84

mṛteṣu vātha jāteṣu brāhmaṇānāṃ dvijottama /
ādantajananāt sadya ācūḍādekarātrakam //

upon deaths or births among brāhmaṇas, O best of the twice-born. / Before the eruption of teeth [purification is] immediate; up to the tonsure rite, [impurity lasts] one night;