Shatapatha Brahmana 2.5.2.10

2.5.2.10

vāruṇyuttarā bhavati | varuṇo ha vā asya prajā agṛhṇāttatpratyakṣaṃ varuṇapāśātprajāḥ pramuñcati mārutī dakṣiṇājāmitāyai nveva mārutī bhavati jāmi ha kuryādyadubhe vāruṇyau syātāmato ha vā asya dakṣiṇato marutaḥ prajā ajighāṃsaṃstānetena bhāgenāśamayattasmānmārutī dakṣiṇā

The northern one is offered to Varuna, since it was Varuna who seized his (Pragâpati's) creatures: hence he thereby directly delivers them from Varuna's noose. The southern one is offered to the Maruts. It is for the sake of diversity that it is offered to the Maruts; for a repetition he would undoubtedly commit, were he to offer both to Varuna. Moreover, it was from the south that the Maruts intended to slay his (Pragâpati's) creatures, and with that share he propitiated them: for this reason the southern (oblation of curds) belongs to the Maruts.