1 Kings 13:18 (KJV) He said unto him, I am a prophet also as thou art; and an angel spake unto me by the word of the LORD, saying, Bring him back with thee into thine house, that he may eat bread and drink water. But he lied unto him.

Have a read of the whole chapter of 1 Kings 13 to get a full picture of what is happening here. The words spoken in verse 18 came from an apostate prophet to deceive the real prophet of GOD who confronted, prophesied and GOD split the altar in two to Jeroboam. The instructions to that prophet, from GOD, were:

“1 Kings 13:16-17 (KJV) And he said, I may not return with thee, nor go in with thee: neither will I eat bread nor drink water with thee in this place: [17] For it was said to me by the word of the LORD, Thou shalt eat no bread nor drink water there, nor turn again to go by the way that thou camest.”

Temptation came through the apostate prophet to cause the real prophet to disobey. In the Defender’s Study Bible it tells us “This prophet was an apostate prophet even before he lied to God’s true prophet, for he was apparently quite content to remain associated with the pagan religion which Jeroboam had set up at Bethel. ”. Regrettably the prophet let himself be deceived and paid the price. “1 Kings 13:23-24 (KJV) And it came to pass, after he had eaten bread, and after he had drunk, that he saddled for him the ass, to wit, for the prophet whom he had brought back. [24] And when he was gone, a lion met him by the way, and slew him: and his carcase was cast in the way, and the ass stood by it, the lion also stood by the carcase.”

There are many lessons for us here and one of them is that we are warned to not believe every spirit. “1 John 4:1 (KJV) Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.” Even if it was claimed that messages came from angels by another so called prophet. “Galatians 1:6-9 (KJV) I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel: [7] Which is not another; but there be some that trouble you, and would pervert the gospel of Christ. [8] But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. [9] As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed.”.
“2 Corinthians 11:13-15 (KJV) For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ. [14] And no marvel; for Satan himself is transformed into an angel of light. [15] Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works.”

Therefore be encouraged to not let yourself be deceived but stand firm on the revealed Word of God (especially the bible) even a so called believer tells you otherwise.
“Matthew 24:24 (KJV) For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.”. We need to know the Word of God and learn how to study and understand it. “2 Timothy 2:15 (KJV) Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.”

Always, let us be strong in the LORD, putting on His amor, submitting ourself to Him and resisting the devil, as it is written:
“Ephesians 6:10-12 (KJV) Finally, my brethren, be strong in the Lord, and in the power of his might. [11] Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. [12] For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.”
“James 4:7 (KJV) Submit yourselves therefore to God. Resist the devil, and he will flee from you.”