Shatapatha Brahmana 6.5.4.10

6.5.4.10

atha mitrasya carṣaṇīdhṛta iti | maitreṇa yajuṣopanyācarati yāvatkiyaccopanyācarati na vai mitraṃ kaṃ cana hinasti na mitraṃ kaścana hinasti tatho haiṣa etāṃ na hinasti no etameṣā tāṃ divaivopavapeddivodvapedaharhyāgneyam

And as often as he attends to (the fire by adding fresh fuel) he attends to it with the prayer relating to Mitra, '[The protection] of Mitra, the preserver of men...;' for a friend (mitra) does not injure any one, nor does any one injure his friend; and in like manner does this one not injure that (fire-pan), nor does it (injure) him. By day he should put (fuel) on it, by day he should clear it (of the ashes).