na vidanti jana yam vai
so ’sav iti na veti ca
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Neither by that saintly person’s activities, by his bodily features, by his words nor by the symptoms of his varnasrama status could people understand whether he was the same person they had known.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The inhabitants of that particular place on the bank of the Kaveri in the valley of the mountain known as Sahya were unable to understand whether that saint was the same man they had known. It is therefore said, vaisnavera kriya mudra vijñe na bhujhaya. A highly advanced Vaisnava lives in such a way that no one can understand what he is or what he was. Nor should attempts be made to understand the past of a Vaisnava. Without asking the saintly person about his previous life, Prahlada Maharaja immediately offered him respectful obeisances.