Abu Dawud
The Office Of The Judge
Book Number: 018 / Hadith Number: 3579
Narated By Umar ibn al-Khattab : Umar said while he was (sitting) on the pulpit: O people, the opinion from the Apostle of Allah (pbuh) was right, because Allah showed (i.e. inspired) him; but from us it is sheer conjecture and artifice.