It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Holy Prophet (peace and blessings of Allah be upon him) said: When a slave fulfills the rights of both Allah and his master, he will receive double reward for every deed. Hazrat Abu Huraira (may Allah be pleased with him) says that I narrated this hadith to Ka'b al-Ahbar, so Ka'b added from his own side that there will be no reckoning for him and for the believer who is indifferent to the world.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 7428