Śatapatha Brāhmaṇa ("of a hundred paths") 3.4.4.9

3.4.4.9

agnīṣomau vai devānāṃ sayujau | tābhyāṃ sārdhaṃ gṛhṇāti viṣṇava ekākine 'nyataramevāghāramāghārayati yaṃ sruveṇa pratikrāmati vā uttaramāghāramāghāryābhijityā abhijayānīti tasmādanyataramevāghāramāghārayati yaṃ sruveṇa

Agni and Soma verily are yoke-fellows among the gods: for these two he takes (ghee) in common. For Vishnu (he takes) singly. He makes only the one libation (âghâra) which (he makes) with the dipping-spoon (sruva). For when he has made the northern (higher) libation he retires: 'May I conquer for conquest' so he thinks, and therefore he makes only the one libation, that with the dipping-spoon.