Śatapatha Brāhmaṇa ("of a hundred paths") 2.2.2.2

2.2.2.2

sa eṣa yajño hato na dadakṣe | taṃ devā dakṣiṇābhiradakṣayaṃstadyadenaṃ dakṣiṇābhiradakṣayaṃstasmāddakṣiṇā nāma tadyadevātra yajñasya hatasya vyathate tadevāsyaitaddakṣiṇābhirdakṣayatyatha samṛddha eva yajño bhavati tasmāddakṣiṇā dadāti

When slain, that sacrifice was no longer vigorous. By means of dakshinâs (gifts to the priests) the gods again invigorated it: hence the name dakshinâ, because thereby they invigorated (dakshay) that (sacrifice). Whatever, therefore, fails in this sacrifice when slain, that he now again invigorates by means of gifts to the priests; whereupon the sacrifice becomes successful: for this reason he makes gifts to the priests.