Musnad Ahmad 4:21

Hashim ibn al-Qasim narrated to us, Layth narrated to us, Zuhrah ibn Ma'bad al-Qurashi narrated to us, from Abu Salih, the freed slave of Uthman, who said: I heard Uthman saying upon the pulpit: "O people, I have concealed from you a hadith that I heard from the Messenger of Allah, may Allah bless him and grant him peace, out of dislike that you might disperse from me. Then, it appeared to me now that I should narrate it to you, so that a man may choose for himself what appears to him. I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: 'A day of guarding in the way of Allah is better than a thousand days in other than it of places.'"