Sai himself was very fond of remembering and singing God's name. He always uttered "Allah Malik" and in His presence made others sing God's name continuously day and night, for all 7 days of the week. This is called 'Naamsaptah'.
Das Ganu Maharaj was not sure of Lord Vitthal's appearance, if he successfully completes the Naamsaptah.
Sai assured him by these words, "Only when the devotee is bursting with love and devotion, Vitthal will manifest Himself here(Shirdi)."
