Musnad Ahmad 850:3

Isma'il narrated to us, Yunus narrated to us, from al-Hasan, from 'Abd al-Rahman ibn Samurah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to me: "O 'Abd al-Rahman, do not ask for authority, for if you are given it upon asking, you will be left to it; and if you are given it without asking, you will be aided in it. And if you swear an oath, then see something else that is better than it, then come to that which is better, and offer expiation for your oath."