A very pathetic incident happened in 1 Kings chapter 13. A man of God was told by God to go and prophesy against the altar Jeroboam had set up in Bethel, he was given instructions from God not to eat or drink anything there, nor return by the same way which he came. But what happened? An old prophet came and told him that the Lord has told him to bring him to his house so that he can eat bread and drink water, but he lied to him.
He followed him, disregarding what he originally heard from God, and not even bothering to ask God if He is truly the one that sent the old prophet. But as he was eating and drinking, the Lord now truly spoke through the old prophet and told him that because he has disobeyed the voice of the Lord, and have come back to eat and drink where he was told not to eat or drink, his body shall not come to grave of his fathers. Of course a lion met him on his way back and slew him.
What a great lesson for Christians! We often depend on "my pastor told me", "that prophet told me that God said this or that" What about you? What has God told you? Some that are even sure they heard clearly from God still abandon what God has told them and follow the one their pastor or prophet told them, without even bothering to ask God if He's truly the one that gave that message to the prophet. If God has changed that thing he told you before, let Him tell you, before you leave what God has told you and start doing what your prophet told you that God said.
"My pastor/prophet said" has led many people completely out of the will of God for their lives. Even in marriage, you hear people say "my pastor/prophet said that that man or that lady is my husband/wife". But what did God tell you? Note that some pastors/prophets lie in the name of the Lord today just like the old prophet did. They can be influenced by money to tell you what you want to hear or tell you that 'God said' when God has not said.
I'm not saying everything your pastor or prophet says is not from God, some of them are truly from God because there are still true prophets, but also learn to hear from God yourself, so you wont fall a victim of false prophesy. God speaks to people in different ways, and if you exercise your inner man to discern His voice, you will know when He's speaking to you. He also speaks through His Word, just like when you are studying the Bible and a particular verse that addresses your situation keep ringing in your heart, that's God speaking to you too.