Rigveda 7.087.04

Varuṇa said to my wise one: three and seven mighty names he bears. The knower of the secret did not tell you of the era; the priest above taught for the generation.

Varuṇa thus spoke to me, possessed of understanding; the cow (speech) has thrice sevenappellations; the wise and intelligent Varuṇa, giving instrumental uction to me, his worthy disciple, had declared themysteries of the plural ce (of Brahma).

To me who understand hath Varuna spoken, the names borne by the Cow are three times seven. The sapient God, knowing the place's secret, shall speak as 'twere to teach the race that cometh.