Musnad Ahmad 26:623

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Mansur and Sulayman, from Ibrahim, from 'Ubaydah al-Salmani, from 'Abdullah, from the Prophet, peace and blessings of Allah be upon him, that he said: "The best of you are my generation, then those who follow them, then those who follow them. Then there will come a people whose testimonies will precede their oaths, and their oaths will precede their testimonies."