Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.1.10

13.4.1.10

prātarāhutyāṃ hutāyāṃ adhvaryuḥ pūrṇāhutiṃ juhoti sarvaṃ vai pūrṇaṃ sarvamaśvamedhaḥ sarvasyāptyai sarvasyāvaruddhyai tasyāṃ vareṇa vācaṃ visṛjate varaṃ dadāmi brahmaṇa iti sarvaṃ vai varaḥ sarvamaśvamedhaḥ sarvasyāptyai sarvasyāvaruddhyai

When the morning offering has been performed, the Adhvaryu performs a full-offering with a view to his (the Sacrificer's) gaining and securing everything, for the full means everything, and the Asvamedha is everything. At this (offering) he releases speech by (bestowing) a boon, saying, 'I grant a boon to the Brahman (priest):' (this he does) with a view to his gaining and securing everything, for a boon is everything, and the Asvamedha is everything.