Sahih Muslim Introduction 82
Ahmad bin Yūsuf al-Azdī narrated to me, he said, I heard Abd ar-Razzāq saying:
‘I did not see Ibn al-Mubārak express so plainly the charge of ‘lying’ except towards Abd ul-Quddūs; for indeed I heard him saying to him ‘[You are] a liar’.’
وَحَدَّثَنِي أَحْمَدُ بْنُ يُوسُفَ الأَزْدِيُّ، قَالَ سَمِعْتُ عَبْدَ الرَّزَّاقِ، يَقُولُ مَا رَأَيْتُ ابْنَ الْمُبَارَكِ يُفْصِحُ بِقَوْلِهِ كَذَّابٌ إِلاَّ لِعَبْدِ الْقُدُّوسِ فَإِنِّي سَمِعْتُهُ يَقُولُ لَهُ كَذَّابٌ ‏.‏