Al-Muzanni reported: Al-Shafi’i, may Allah have mercy on him, heard me one day as I said, “This narrator is a great liar!” Al-Shafi’i said to me, “O Abu Ibrahim, dress your words in the best manner. Do not say this narrator is a great liar, but rather say his narrations are of no importance.”
Source: Fatḥ al-Mughīth 2/127
عَنِ الْمُزَنِيِّ قال سَمِعَنِي الشَّافِعِيُّ رحمه الله يَوْمًا وَأَنَا أَقُولُ فُلَانٌ كَذَّابٌ فَقَالَ لِي يَا أَبَا إِبْرَاهِيمَ اكْسُ أَلْفَاظَكَ أَحْسَنَهَا لَا تَقُلْ فُلَانٌ كَذَّابٌ وَلَكِنْ قُلْ حَدِيثُهُ لَيْسَ بِشَيْءٍ
2/127 فتح المغيث