Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.40

6.2.2.40

tadāhuḥ | dadyādetasminyajñe dakṣiṇāṃ nenme 'yaṃ yajño 'dakṣiṇo 'sadbrahmaṇa ādiṣṭadakṣiṇāṃ dadyādbrahmā vai sarvo yajñastadasya sarvo yajño bhiṣajjayito bhavatīti na tathā kuryādiṣṭakāṃ vā etāṃ kurute tadyatheṣṭakāyāmiṣṭakāyāṃ dadyāttādṛktadamurhyeva dadyādyadasyopakalpeta

Here now they say, 'At this sacrifice he should give a Dakshinâ (sacrificial gift); thinking, "Lest my sacrifice should be without a dakshinâ!" let him give to the Brahman the prescribed dakshinâ, for the Brahman is the entire sacrifice: thus the entire sacrifice of his becomes healed.' Let him not do so; for he makes this a brick, and it would be just as if he were to give a present with each brick: only at that (proper) time let him therefore give what it befits him (to give).