Is it permissible for brothers to agree that whoever performs a certain act is obligated to provide dinner at his own expense?

This image represents a form of gambling that is forbidden by Islamic law. Gambling with money is not permissible except in cases specifically exempted by the Lawgiver, which are horse racing, camel racing, and archery. Anything other than these is forbidden because it constitutes consuming wealth unjustly and is a form of maysir (gambling). As for a person saying, "If this matter is accomplished for me, then you will have such-and-such from me," this is a form of promise, and fulfilling it is prescribed (or legitimate).