Sunan an-Nasa'i 4151
It was narrated that 'Ubadah said:
"We pledged to the Messenger of Allah to hear and obey both in times of hardship and ease, when we felt energetic and when we felt tired, that we would   not contend with the orders of whomever was entrusted with it, that we would speak the truth or stand firm in the way of truth wherever we may be, and that we would not fear the blame of the blamers."
أَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، وَالْحَارِثُ بْنُ مِسْكِينٍ، قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، عَنِ ابْنِ الْقَاسِمِ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، قَالَ أَخْبَرَنِي عُبَادَةُ بْنُ الْوَلِيدِ بْنِ عُبَادَةَ، قَالَ حَدَّثَنِي أَبِي، عَنْ عُبَادَةَ، قَالَ بَايَعْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى السَّمْعِ وَالطَّاعَةِ فِي الْيُسْرِ وَالْعُسْرِ وَالْمَنْشَطِ وَالْمَكْرَهِ وَأَنْ لاَ نُنَازِعَ الأَمْرَ أَهْلَهُ وَأَنْ نَقُولَ - أَوْ نَقُومَ - بِالْحَقِّ حَيْثُمَا كُنَّا لاَ نَخَافُ لَوْمَةَ لاَئِمٍ ‏.‏