What is the ruling on the additional salary resulting from a false certificate of experience, and how can one purify their income from it?

Falsifying experience certificates or other documents is forbidden (haram), whether done by the person himself or if he agrees for someone else to do it on his behalf. The questioner and his brother must repent to Allah and resolve not to return to such an action. The salary earned from working with this document is permissible (mubah) if the person possesses sufficient experience and performs his work as required.