Garudapurana 1.34.43

1.34.43

brahmāṇaṃ nāradaṃ siddhaṃ guruṃ paraguruṃ tathā /
gurośca pāduke tadvatparamasya gurostathā //

Brahmā, Nārada, the Siddha, the guru, and the supreme guru, / and likewise the sandals of the guru and of the supreme guru;