I need to make something very clear: the Bible does not list the requirements of a prophet. I can list some guidelines, but these are not absolutes.
The Old Testament tells us the bizarre story of Balaam, who was paid to curse Israel but was forced to bless them instead. In Numbers 24, a distraught Balaam explains why he couldn't curse Israel:
12 So Balaam said to Balak, "Did I not also speak to your messengers whom you sent to me, saying,
13 'If Balak were to give me his house full of silver and gold, I could not go beyond the word of the LORD, to do good or bad of my own will. What the LORD says, that I must speak'?
If you want the gift of prophecy, you need to get something straight: you can only say what God tells you to say, whether you like it or not.