Sahih Bukhari Volume 9, Book 93, Hadith 7149

حَدَّثَنَا أَبُو مَعْمَرٍ، حَدَّثَنَا عَبْدُ الْوَارِثِ، حَدَّثَنَا يُونُسُ، عَنِ الْحَسَنِ، قَالَ حَدَّثَنِي عَبْدُ الرَّحْمَنِ بْنُ سَمُرَةَ، قَالَ قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ يَا عَبْدَ الرَّحْمَنِ بْنَ سَمُرَةَ، لاَ تَسْأَلِ الإِمَارَةَ، فَإِنْ أُعْطِيتَهَا عَنْ مَسْأَلَةٍ وُكِلْتَ إِلَيْهَا، وَإِنْ أُعْطِيتَهَا عَنْ غَيْرِ مَسْأَلَةٍ أُعِنْتَ عَلَيْهَا، وَإِذَا حَلَفْتَ عَلَى يَمِينٍ فَرَأَيْتَ غَيْرَهَا خَيْرًا مِنْهَا، فَأْتِ الَّذِي هُوَ خَيْرٌ، وَكَفِّرْ عَنْ يَمِينِكَ ‏"

Narrated By 'Abdur-Rahman bin Samura : Allah's Apostle said, "O 'Abdur-Rahman bin Samura! Do not seek to be a ruler, for if you are given authority on your demand, you will be held responsible for it, but if you are given it without asking for it, then you will be helped (by Allah) in it. If you ever take an oath to do something and later on you find that something else is better, then do what is better and make expiation for your oath."