Soma is a drink, derived from a plant that's now unknown, that played an crucially important role in Vedic ritual; the Soma Yagna, in which Soma was offered to the gods, is extensively discussed in the Vedas and it was the chief Vedic method of worshipping the gods. The god of this drink is Chandra the moon god, and in his capacity as the god of the Soma drink he is often called Soma, Pavamana, or Indu. Here is a verse from the Ninth Mandala of the Rig Veda (often called the Soma Mandala) in praise of him:
Winning the friendship of the Deities, Indu flows in a thousand streams to make them joyful. Praised by the men after the ancient statute, he hath come nigh, for our great bliss, to Indra.
My question is, what is this "ancient statute" about praising Soma? The verses of the Rig Veda are already of timeless antiquity, having been heard by sages directly from the gods from time immemorial. So what statute is so old that it's even considered ancient by a Rig Vedic verse?