Garudapurana 1.209.12

1.209.12

Vṛttā is two na-gaṇas, sa, and two heavies; samadrikā is two na-gaṇas, ra, la, and a heavy;
śyenikā is ra, ja, ra, la, and ga; śikhaṇḍita is ja, sa, ta, and two heavies;
the triṣṭubh metre has thus been declared by the high-souled Piṅgala.