إثبات المتأخر

However, I should note that "retarded" in English can be considered offensive when referring to people. If this is technical terminology in a specific context (such as a delayed signal or a programming concept), a more appropriate translation might be:

**إثبات التأخير** (Proof of Delay)

or

**إثبات المتأخر** (Proof of Lag/Delay)

Please provide more context if you need a more precise translation.