Śatapatha Brāhmaṇa ("of a hundred paths") 3.4.1.5

3.4.1.5

tadu tathā na kuryāt vimucyaiva prapādya gṛhṇīyādyathā vai devānāṃ caraṇaṃ tadvā anu manuṣyāṇāṃ tasmānmānuṣe yāvanna vimuñcate naivāsmai tāvadudakaṃ haranti nāpacitiṃ kurvantyanāgato hi sa tāvadbhavatyatha yadaiva vimuñcate 'thāsmā udakaṃ harantyathāpacitiṃ kurvanti tarhi hi sa āgato bhavati tasmādvimucyaiva prapādya gṛhṇīyāt

Let him, however, not do this but let him take out (the material for offering) only after unyoking (both oxen) and after making (Soma) enter (the hall); for the ways of men are in accordance with those of the gods. And accordingly, in human practice, so long as (a guest) has not unyoked, people do not bring water to him and show him no honour, for so long he has not yet arrived; but when he has unyoked, then they bring him water and show him honour, for then he has indeed arrived: let him therefore take out (the material for offering) only after unyoking and after making (Soma) enter (the hall).