Gobhilagrihyasutra 2.9.8

2.9.8

atha mātā śucinā vasanena kumāram ācchādya paścād agner udagagreṣu darbheṣu prācy upaviśati;

Then the mother, having dressed the son in a clean garment, sits down to the west of the fire on northward-pointed Darbha grass, facing the east.