Sahih Bukhari Volume 9, Book 89, Hadith Number 263.

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.”