Gobhilagrihyasutra 2.9.16

2.9.16

yena pūṣā bṛhaspater iti triḥ prāñcaṃ prohaty apracchindan, sakṛd yajuṣā, dvis tūṣṇīm.

With (the Mantra), 'With which Pûshan has shaven Brihaspati's head' (ibid. 7), he moves forward (that razor or the mirror) three times towards the east without cutting (the hair); once with the Yagus, twice silently.