Devibhagavatapurana 3.17.38

3.17.38

tadā'sau pañcame varṣe prāpya mantramanuttamam |
ṛṣicchandovihīnañca dhyānanyāsavivarjitam ||

The son of the king, when he was five years old, got this most excellent mantra, though without its Risi (seer), meditation, without its chhanda (metre) and without Nyâsa (assignment of the various parts of the body to different deities, accompanied with prayers and corresponding gesticulations), and considered this as the quintessence of all, therefore meditated this always in his mind spontaneously and never forgot it.