Matthew Poole and continuators on 1 Kings 11:29

29 And it came to pass at that time, when Jeroboam went out of Jerusalem , that the prophet Ahijah the Shilonite found him in the way, and he had clad himself with a new garment; and they two were alone in the field .

Upon some occasion, possibly to execute his charge.

Having gone aside thither for some private conference; for otherwise it is most likely that he had Servants attending upon him, who, though they heard not the words, yet might see the action, and the rending of Ieroboam's Coat; and thus it came to Solomon's ears, who being so acute and wise, could easily understand the thing by what he heard of the action, especially when a Prophet did it.