Sunan an-Nasa'i, Hadith 4187 ⓘ
It was narrated that Ibn 'Umar said: "We used to pledge to the Messenger of Allah to hear and obey, the he said: 'In as much as you can."'
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، ح وَأَخْبَرَنِي عَلِيُّ بْنُ حُجْرٍ، عَنْ إِسْمَاعِيلَ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ كُنَّا نُبَايِعُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى السَّمْعِ وَالطَّاعَةِ ثُمَّ يَقُولُ " فِيمَا اسْتَطَعْتَ " . وَقَالَ عَلِيٌّ " فِيمَا اسْتَطَعْتُمْ " .
also referenced under: Book 39, Hadith 39 (In-Book) & Volume 5, Book 39, Hadith 4192 (DarusSalam)