YV 4.2g

When the Yatis were being eaten, their heads fell away; they became Kharjuras; their sap rose upwards, they became Kariras; the Kariras are connected with Soma; the offering connected with Soma makes rain to move from the sky; in that there are Kariras (in the sacrifice) [2], by means of an offering which is connected with Soma he wins the rain from the sky. With honey he unites (them); honey is the sap of the waters and the plants; verily it rains from the waters and the plants; verily also he brings down rain from the waters and the plants. 'Gladdening, obedient', (with these words) he unites (them); verily he approaches them by their names; just as one may say, 'Come hither, N. N.', so by their names [3] he makes them move forward. Thou art the fetter of the strong horse; for rain I yoke thee', he says the horse is strong, Parjanya is strong; becoming black as it were he rains; verily he unites him with his hue, to win the 'O gods having wealth, O gods granting protection, O gods drinking together', (with these words) he ties on; verily by means of the gods he daily seeks rain. If it should rain, so much only should be offered; if it should not rain, on the next day he should offer an oblation. Mitra and Varuna are day and night, by day and night Parjanya rains, for by night or by day he rains; verily he has recourse to Mitra and Varuna with their own share; verily they [1] make Parjanya rain for him by day and night. To Agni, hiding his abode, he should offer a cake on eight potsherds, to the Maruts on seven potsherds, to Surya on one potsherd; Agni thence causes the rain to arise, the Maruts lead it out when produced; when yonder Sun Moves low with his rays, then he rains; becoming a hider of his abode, as it were, he rains; these deities are the lords of rain; them he has recourse to with their own share; they [2] make Parjanya rain for him; even if he is not minded to rain yet he rains.