Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.1.14

3.8.1.14

tadyatrainaṃ viśasanti | tatpurastāttṛṇamupāsyati varṣo varṣīyasi yajñe yajñapatiṃ dhā iti barhirevāsmā etatstṛṇātyaskannaṃ havirasaditi tadyadevāsyātra viśasyamānasya kiṃcitskandati tadetasminpratitiṣṭhati tathā nāmuyā bhavati

In front of the place where they cut it up, he throws down a stalk of grass, with, 'O great one, lead the lord of sacrifice unto greater sacrifice!' he thus strews barhis (an underlayer of sacrificial grass) for it, that no sacrificial food may be spilt; whatever may now be spilt of it when it is cut up, that settles thereon and thus is not lost.