Mishkat al-Masabih 18 The Offices of Commander and Qadi كتاب الإمارة والقضاء 7

وَعَنِ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا قَالَ: كُنَّا إِذَا بَايَعْنَا رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَلَى السَّمْعِ وَالطَّاعَةِ يَقُولُ لَنَا: «فِيمَا اسْتَطَعْتُمْ»

Ibn ‘Umar told that when they swore allegiance to God’s Messenger to hear and obey he was saying to them, “In what you are able.” (Bukhari and Muslim.)