Is it permissible to delay returning the greeting of "peace" to someone with whom I have personal enmity, or must I return it immediately?

The Hanafis and Shafi'is hold that returning the greeting of salam must be done immediately. If one delays returning the salam without a valid excuse, it is considered a reprehensible (makruh tahrimi) act. The sin is not lifted by merely returning the salam, but by repenting.