Musnad Ahmad 26:667

Waki' narrated to us, Al-A'mash narrated to us, from Ibrahim, from 'Ubaydah, from 'Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of people are my generation, then those who follow them, then those who follow them. Then a people will come whose testimonies will precede their oaths, and their oaths will precede their testimonies."