Sunan an-Nasa'i, Volume 5, Book 39, Hadith 4193 (DarusSalam) ⓘ
Ibn 'Umar said: "When we gave our pledge to the Messenger of Allah to hear and obey, he would say to us: 'In as much as you can".
أَخْبَرَنَا الْحَسَنُ بْنُ مُحَمَّدٍ، قَالَ حَدَّثَنَا حَجَّاجٌ، عَنِ ابْنِ جُرَيْجٍ، قَالَ أَخْبَرَنِي مُوسَى بْنُ عُقْبَةَ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ كُنَّا حِينَ نُبَايِعُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى السَّمْعِ وَالطَّاعَةِ يَقُولُ لَنَا " فِيمَا اسْتَطَعْتُمْ " .
also referenced under: Hadith 4188 (Reference) & Book 39, Hadith 40 (In-Book)