Sahih Bukhari Volume 9, Book 93, Hadith 7151

حَدَّثَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ بُرَيْدٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِي مُوسَى ـ رضى الله عنه ـ قَالَ دَخَلْتُ عَلَى النَّبِيِّ صلى الله عليه وسلم أَنَا وَرَجُلاَنِ مِنْ قَوْمِي فَقَالَ أَحَدُ الرَّجُلَيْنِ أَمِّرْنَا يَا رَسُولَ اللَّهِ‏.‏ وَقَالَ الآخَرُ مِثْلَهُ‏.‏ فَقَالَ ‏"‏ إِنَّا لاَ نُوَلِّي هَذَا مَنْ سَأَلَهُ، وَلاَ مَنْ حَرَصَ عَلَيْهِ ‏"‏‏

Narrated By Abu Musa : Two men from my tribe and I entered upon the Prophet. One of the two men said to the Prophet, "O Allah's Apostle! Appoint me as a governor," and so did the second. The Prophet said, "We do not assign the authority of ruling to those who ask for it, nor to those who are keen to have it."