Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) used to say (upon performing the funeral prayer over someone): "O Allah, You are its Lord; You created it; You guided it to Islam; You have taken its life back and You are most knowledgeable of its hidden and apparent affairs. We have come as intercessors for him, so forgive him."
شرح الحديث :
When the Prophet (may Allah's peace and blessings be upon him) performed the funeral prayer over someone, he would say what means: O Allah, You are the master and owner of this person, You created him, You guided him to Islam, You are the One Who has taken his soul, You are more knowledgeable than him about his secret and apparent affairs. We have come before You to make supplication for this person to receive forgiveness, so, forgive him, for indeed you are the One who answers supplications.