Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.1.10

1.3.1.10

sa vai tathaiva sammṛjyāt | yathāgniṃ nābhivyukṣedyathā yasmā aśanamāhariṣyantsyāttam pātranirṇejanenābhivyukṣedevaṃ tattasmādu tathaiva sammṛjyādyathāgniṃ nābhivyukṣetprāṅivaivotkramya

Let him brush, them so as not to spatter anything towards the fire, as he would thereby bespatter him, to whom he will be bringing food, with the slops of the vessels: therefore let him brush them so as not to spatter anything towards the fire, that is to say, after stepping outside (the Âhavanîya fire-house) towards the east.