1 Kings 13:5

The altar also was rent, and the ashes poured out from the altar, according to the sign which the man of God had given by the word of the Lord.

Cross-reference

1 Kings 13:3 gives the sign — altar split and ashes poured — which is exactly fulfilled in verse 5.

1 Kings 13:1 introduces the man of God who delivered the prophecy; the altar sign in verse 5 is the immediate fulfillment of his word.

Deuteronomy 18:22 gives the test of a true prophet: sign must come true. Here, it does — confirming the man of God's authenticity.

Mark 16:20 shows signs confirming the word preached — similar to how the torn altar confirmed the man of God's prophecy.