If a person appoints someone to be his agent to perform all his tasks for him, it is valid. However, if he appoints him to be his agent to perform one of his tasks for him but does not specify which task, the agency is not valid. But, if he appoints him to be his agent to perform one of a number of tasks at the agent’s discretion – for example, he appoints him as his agent to either sell his house or give it on rent (ijārah) – the agency is valid.