Verse 2.3.1.17

atha caturunnayati | caturdhāvihitaṃ hīdam payo'tha samidhamādāyodādravati samiddhahomāyaiva so'nupasādya pūrvāmāhutiṃ juhoti sa yadupasādayedyathā yasmā aśanamāhariśyantsyāttadantarā nidadhyādevaṃ tadatha yadanupasādya yathā yasmā aśanamāharettasmā āhṛtyaivopanidadhyādevaṃ tadupasādyottarāṃ nānāvīrye evaine etatkaroti manaśca ha vai vākcaite āhuti tanmanaścaivaitadvācaṃ ca vyāvartayati tasmādidam manaśca vākca samānameva sannāneva

Preview of English translation:

17. Thereupon he ladles four times (milk with the sruva into the Agnihotra ladle), for in a fourfold way was that milk supplied. He then takes a kindling-stick (samidh), and hastes up (to the Ahavaniya, with the ladle) to make the libation on the burning (stick). He offers the first libation (purvahuti) without putting down (the spoon) beside (the fire, on the grass-bunch). For, were he to put it down beside (the fire), it would be as if, in taking food to somebody, one were to put it down on one’s way thither. But when (he makes the libation) without previously putting it down, it is as if, in taking food to somebody, one puts it down only after taking it to him. The second (libation he then makes) after putting it down: he thereby makes these two (libations) of various vigour. Now these two: libations are mind and speech: hence he thereby separates mind and speech from each other; and thus mind and speech, even while one and the same (samana), are still distinct (nana).

For a detailled translation, including proper diacritics and footnotes, go the full English translation.