BṚHADĀRAṆYAKA UPANISHAD · 6.4.26

अथास्य नाम करोति वेदो ऽसीति ।
तद् अस्यैतद् गुह्यम् एव नाम भवति ॥

athāsya nāma karoti vedo ’sīti ।
tad asyaitad guhyam eva nāma bhavati ॥

Then he gives him a name, saying: 'You are Veda.' So this becomes his secret name.

Robert Ernest Hume · The Thirteen Principal Upanishads (1921), Bṛhadāraṇyaka VI.4