Śatapatha Brāhmaṇa ("of a hundred paths") 5.5.4.35

5.5.4.35

tasya napuṃsako gaurdakṣiṇā | na vā eṣa strī na pumānyannapuṃsako gauryadaha pumāṃstena na strī yadu strī teno na pumāṃstasmānnapuṃsako gaurdakṣiṇāśvā vā rathavāhī sā hi na strī na pumānyadaśvā rathavāhī yadaha rathaṃ vahati tena na strī yadu strī teno na pumāṃstasmādaśvā rathavāhī dakṣiṇā

A castrated bull is the sacrificial fee for this (sacrifice);--the castrated bull is neither female nor male; for being a male it is not a female, and being a female (unmanned) it is not a male: therefore a castrated bull is the fee. Or a draught-mare;--the draught-mare is neither male nor female; for in that it pulls the cart it is not a female; and being a female, it is not a male: therefore a draught-mare (may be) the fee.