Put up or shut up!
1. Inf. a command to prove something or stop talking about it; Do something or stop promising to do it! I'm tired of your telling everyone how fast you can run. Now, do it! Put up or shut up! Now's your chance to show us that you can run as fast as you can talk. Put up or shut up!
2. Inf. a command to bet money in support of what one advocates. If you think that your horse is faster than mine, then make a bet. Put up or shut up! You think you can beat me at cards? Twenty bucks says you're wrong. Put up or shut up!