Musannaf Ibn Abi Shayba 27:776

'Affan narrated to us, he said: Hammad bin Salamah narrated to us, from al-Jurayri, from Abu Nadrah, from 'Abdullah bin Mawlah, he said: I was walking with Abu Burdah al-Aslami, and he said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "The best of this nation is the generation in which I was sent, then those who follow them, then those who follow them, then those who follow them. Then there will be among them a people whose testimonies will precede their oaths, and their oaths will precede their testimonies."