Sayyiduna Ubadah bin Samit (may Allah be pleased with him) says: We pledged allegiance to the Messenger of Allah (peace and blessings of Allah be upon him) to listen and obey in happiness and displeasure, and that we would not dispute with the rulers for authority, and that wherever we may be, we would speak the truth, and we would not fear the blame of any blamer in the matter of Allah.
Narrated Abdullah bin Umar (may Allah be pleased with them) that: When we pledged allegiance to the Messenger of Allah (peace be upon him) to listen and obey, the Prophet (peace be upon him) would say to us: "As much as you are able." (That is, you should act upon it only as much as you have the ability.)