John Gill Commentary 1 Kings 13:17

"for it was said to me by the word of Jehovah, Thou shalt eat no bread nor drink water there, nor turn again to go by the way that thou camest." — 1 Kings 13:17 (ASV)

For it was said to me by the word of the Lord
By the angel that was sent to him, who gave him his message and instructions; which he was persuaded came from the Lord himself, and therefore looked upon himself under obligation to regard them as such:

you shall eat no bread
the same that he observed to the king, (1 Kings 13:9) .