द्यौरेवर्गादित्यः साम तदेतदेतस्यामृच्यध्यूढं साम तस्मादृच्यध्यूढं साम गीयते द्यौरेव सादित्योऽमस्तत्साम ॥ १.६.३ ॥
In plain words
The sky is the Ṛc and the sun is the Sāman. This Sāman rests upon that Ṛc; therefore the Sāman is sung as resting upon the Ṛc. The sky is sā and the sun is ama, and that makes sāman.