Sunan Ibn Majah, Volume 4, Book 24, Hadith 2868 (DarusSalam) ⓘ
It was narrated that ‘Attab, the freed slave of Hurmuz, said: “I heard Anas bin Malik say: ‘We gave our pledge to the Messenger of Allah on the basis that we would listen and obey. He said: “As much as you can.”
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا شُعْبَةُ، عَنْ عَتَّابٍ، - مَوْلَى هُرْمُزَ - قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ، يَقُولُ بَايَعْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى السَّمْعِ وَالطَّاعَةِ فَقَالَ " فِيمَا اسْتَطَعْتُمْ " .
also referenced under: Hadith 2868 (Reference) & Book 24, Hadith 2978 (In-Book)