Who was told by Sai Baba that Vitthal would appear if the devotee was full of faith?

The devotee who received this assurance from Sai Baba was Das Ganu. According to Chapter 4, Baba ordered Das Ganu to organize a Name-week (Saptah). When Das Ganu expressed his desire for Vitthal to appear, Baba placed a hand on His chest and firmly promised, "Yes, yes, the form of Vitthal will appear! But the devotee must be full of faith." Baba explained that one need not travel to Pandhari, as Vitthal would manifest right there in Shirdi out of intense love for the devotee. The text confirms that Das Ganu did receive this promised sight of Vitthal.