Shatapatha Brahmana 4.6.3.1

4.6.3.1

athātaḥ paśvayanasyaiva | paśvekādaśinyaiveyātsa āgneyam prathamam paśumālabhate 'tha vāruṇamatha punarāgneyamevamevaitayā paśvekādaśinyeyāt

Now as to the manner of animal offerings. One may perform with the (ordinary) set of eleven victims. He seizes one for Agni as the first victim, and one for Varuna (as the last); then again one for Agni.: in this way let him perform with the set of eleven victims.