Muwatta Malik 1806
موطأ مالك#1806SahihMalik related to me from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "When a slave gives good counsel to his master and worships Allah correctly, he has his reward twice over
Scholarly Authentication
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Salim al-HilaliSahih
In-book reference: 54:44