Varahashrautasutra 3.2.2.35

3.2.2.35

vāgaitu vāgupaitu vāksametūpa maitu vāk - bhūrbhuvaḥ svarityanvārabhya vācam̐ yacchantyādhivṛkṣasūryādā vā nakṣatradarśanāt

Having touched [it] with "May speech come! May speech approach! May speech assemble! May speech approach me! Bhūr bhuvaḥ svar!", they restrain their speech until the sun is above the trees or until the appearance of the stars.