Kauthumagrihyasutra 14

In the third year tonsure should be performed. The ancestral offering for prosperity is on the preceding day. Then, on the following day, having bathed at dawn, the patron of the sacrifice smears a square sacrificial ground. Having placed [the fire etc.] beginning with the fire for clarified butter to the south outside the circle, the barber sits facing east. Then a vessel with warm water and a mirror; immediately following that, a receptacle for hair; to the west of that, a bundle of darbha grass; to the north, [or] north-west, etc., of the sacrificial ground, having bathed [the boy]; fresh dung of a red bull, common [substances]; a pot-cooked offering of kṛsara, [or] what is cooked for ordinary food, saying: ‘Let there not be a sacrifice in an unfit place.’ Then, having established the domestic fire and offered the morning oblation, in a clan other than his own, in one place he should have a line made [with hair-cutting]. Some [have] three tufts of hair, some five tufts of hair, according to the rule of their clan and family. They should bury the hair in the wilderness; some dispose of it [otherwise]. The young boy having bathed again, the patron of the sacrifice sits down in his own place. Then, having completed the later [rites] and sung the Vāmadevya chant, then the feeding of brahmins; then the feeding of brahmins.

KauthGS 15: