The works of Ādi Śaṅkarācārya

Viṣṇusahasranāmastotram

Verse 577

इतीदम् इत्यनेन नामसहस्रन्यूनानतिरिक्तमुक्तमिति दर्शयति दिव्यानामप्राकृतानां नाम्नां सहस्रं प्रकीर्तित मिति वदता प्रकारान्तरेणापि संख्योपपत्तिर्दर्शिता ।प्रक्रमे 'किं जपन्मुच्यते जन्तुः' इति जपशब्दोपादानात् कीर्तयेत् इत्यनेनापि त्रिविधजपो लक्ष्यते ।उच्चोपांशुमानसलक्षणस्त्रिविधो जपः ॥

In plain words

By stating 'thus this,' the text shows that the thousand divine and unearthly names are complete, lacking nothing and having no excess; the validity of this count is demonstrated through alternative means as well. Since the opening question asks, 'By muttering what does a creature attain freedom?', the injunction 'one should chant' points to a threefold practice: the recitation of names performed aloud, whispered inwardly, or held purely in the mind.

Close to the Sanskrit

Thus this, by this it is shown that the thousand of names, being divine and unearthly, are neither deficient nor excessive, says one, and the validity of the number is shown through another method also. In the context, because of the employment of the word japa in 'What chanting does a creature become free?', by 'one should chant' also the threefold japa is indicated. Japa is threefold, characterized as loud, whispered, and mental.