Sahih al-Bukhari, Book 93, Hadith 62 (In-Book) ⓘ
Narrated `Abdullah bin `Umar: Whenever we gave the Pledge of allegiance to Allah's Messenger for to listen to and obey, he used to say to us, for as much as you can."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ كُنَّا إِذَا بَايَعْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى السَّمْعِ وَالطَّاعَةِ يَقُولُ لَنَا " فِيمَا اسْتَطَعْتَ " .
also referenced under: Hadith 7202 (DarusSalam) & Volume 9, Book 89, Hadith 309 (USC-MSA)