It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that once I asked the Prophet (peace and blessings be upon him): "Which deed is most beloved to Allah?" The Prophet (peace and blessings be upon him) said: "Prayer at its proper time." I asked: "Then what?" He said: "Good treatment of parents." I asked: "Then what?" He said: "Striving in the way of Allah." The Prophet (peace and blessings be upon him) mentioned these things to me, and if I had asked for more, he (peace and blessings be upon him) would have told me more.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4313
Hadith Gradingحکم دارالسلام:حديث صحيح، خ: 527، م: 85، المسعودي- و إن سمع منه يزيد وأبو النضر بعد الاختلاط - متابع بشعبة فى الرواية: 4186.