Albert Barnes Commentary 1 Samuel 11:7

"And he took a yoke of oxen, and cut them in pieces, and sent them throughout all the borders of Israel by the hand of messengers, saying, Whosoever cometh not forth after Saul and after Samuel, so shall it be done unto his oxen. And the dread of Jehovah fell on the people, and they came out as one man." — 1 Samuel 11:7 (ASV)

Though not expressly stated, it is undoubtedly implied that he sent the portions by messengers to the twelve tribes, after the analogy of, and probably in imitation of, Judges 19:29. He used the revered name of Samuel to strengthen his own weak authority. Samuel accompanied Saul on the expedition (1 Samuel 11:12).