Shatapatha Brahmana 9.3.4.11

9.3.4.11

taṃ haike dakṣiṇato 'gnerabhiṣiñcanti | dakṣiṇato vā annasyopacārastadenamannasyārdhādabhiṣiñcāma iti na tathā kuryādeṣā vai dikpitṝṇāṃ kṣipre haitāṃ diśam praiti yaṃ tathābhiṣiñcanti

Some, however, anoint him on the right (south) side of the fire-altar, on the ground that it is from the right side that food is served, and that they thus anoint him from the food-side. But let him not do so, for that (southern) region belongs to the Fathers, and quickly he goes to that region whom they anoint in that way.