Abu Dawud Book 36, Hadith Number 4990.

Narated By Amr ibn al-‘As : One day when a man got up and spoke at length Amr ibn al-‘As said If he had been moderate in what he said: It would have been better for him. I heard the Apostle of Allah (PBUH) say: I think (or, I have been commanded) that I should be brief in what I say, for brevity is better.