"Take this most seriously: A yes on earth is yes in heaven; a no on earth is no in heaven. What you say to one another is eternal. I mean this. When two of you get together on anything at all on earth and make a prayer of it, my Father in heaven goes into action. And when two or three of you are together because of me, you can be sure that I'll be there." Matthew 18: 18-20 MSG
There is power when two or more people agree in prayer. According to this scripture, God is present when you and another person are on one accord. God is ready to make this situation happen. The same principle applies in the negative. The enemy is present to confirm your negative agreement as well. Be careful what you say and who you agree with concerning any situation.