Śatapatha Brāhmaṇa ("of a hundred paths") 3.1.4.2

3.1.4.2

tato yāni trīṇi sruveṇa juhoti | tānyādhītayajūṃṣītyācakṣate sampada eva kāmāya caturthaṃ hūyate 'tha yatpañcamaṃ srucā juhoti tadeva pratyakṣamaudgrabhaṇamanuṣṭubhā hi tajjuhoti vāgghyanuṣṭubvāgghi yajñaḥ

And again, the three libations which he makes with the dipping-spoon (sruva) are said to be 'âdhîtayagus.' The fourth libation is made for the sake of completeness; while the fifth, which is made with the offering-spoon (sruk, viz. the guhû), is the real audgrabhana-libation: for he makes it with an anushtubh verse, and the anushtubh is speech, and the sacrifice also is speech.