Hadith: Whenever we gave the Messenger of Allah (may Allah's peace and blessings be upon him) pledge of allegiance to listen and obey, he would say to us: To the best of your ability

عن ابن عمر رضي الله عنهما قال: كنا إذا بايعنا رسول الله صلى الله عليه وسلم على السمع والطاعة، يقول لنا: «فيما استطعتم».
[صحيح] - [متفق عليه]

Ibn ‘Umar (may Allah be pleased with him) reported: Whenever we gave the Messenger of Allah (may Allah's peace and blessings be upon him) pledge of allegiance to listen and obey, he would say to us: "To the best of your ability."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Ibn ‘Umar informs us that whenever they gave pledge allegiance to the Prophet (may Allah's peace and blessings be upon him) he would order them to listen and obey. He restricted such obedience to what falls within their ability. In other words, if a ruler orders a Muslim to do something that he is not able to do, he does not have to obey him. Allah, the Almighty,, said: {Allah does not charge a soul except [with that within] its capacity.} [Sūrat al-Baqarah: 286]