Agniveshyagrihyasutra 2.5.10.16

2.5.10.16

kṛṣṇamaśvamadbhirabhyukṣati divā cittamaḥ kṛṇvanti parjanyenodavāhena \

He sprinkles the black horse with water [saying:] "Even by day they produce darkness with Parjanya, the bringer of water;