I've heard that Sai Baba instructed one of his devotees to feed a black dog as a remedy for some problem. Who was this devotee and what was the reason for this specific instruction?

Based on the provided texts, there is no mention of Sai Baba telling any devotee to feed a black dog. However, the source material does describe a similar act involving a different devotee and a different animal. According to chapter 0, a devotee named Kashiram carried powdered sugar with him specifically to feed ants. This practice was not advised by Sai Baba, but by another saint named Janakidas Baba. This act was so significant to Kashiram that he considered the bundle of sugar very dear and was willing to risk his life to protect it from robbers.