Hadith 1806
حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الْعَبْدُ إِذَا نَصَحَ لِسَيِّدِهِ وَأَحْسَنَ عِبَادَةَ اللَّهِ فَلَهُ أَجْرُهُ مَرَّتَيْنِ " .
Malik 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
Sahih (Salim al-Hilali)
Muwatta Malik 1806 · Book 54, Hadith 44