Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.26

3.2.2.26

purāstamayādāha | dīkṣita vācaṃ yaceti tāmastamite vācaṃ visṛjate purodayādāha dīkṣita vācaṃ yaceti tāmudite vācaṃ visṛjate saṃtatyā evāharevaitadrātryā saṃtanotyahnā rātrim

Before sunset he (the Adhvaryu) says, 'Consecrated, restrain thy speech!' and after sunset he releases speech. Before sunrise he says, 'Consecrated, restrain thy speech!' and after sunrise he releases his speech,--for the sake of continuity: with the night he continues the day, and with the day the night.