Chapter 1: Introduction
Abd ur-Rahman bin Bishr al-Abdī narrated to me, he said, I heard Muhammad bin Abd Allah bin Ubayd bin Umayr al-Laythī was mentioned near Yahyā bin Sa’īd al-Qattān, so he weakened him severely. Then it was said to Yahyā: ‘More weak than Ya’qūb bin Atā ’?’ He said: ‘Yes’. Then he said: ‘I did not see anyone transmitting on authority of Muhammad bin Abd Allah bin Ubayd bin Umayr’.
Sahih Muslim Introduction 91