It is narrated from Hazrat Anas (may Allah be pleased with him) that I pledged allegiance to the Prophet (peace and blessings be upon him) on the condition of listening and obeying, and the Prophet (peace and blessings be upon him) added the restriction of "as much as you are able."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 13116
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن من أجل عتاب.