Arabic (Original)
أَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ قَالَ سَمِعْتُ أَبَا الْعَبَّاسِ مُحَمَّدَ بْنَ يَعْقُوبَ يَقُولُ سَمِعْتُ الرَّبِيعَ بْنَ سُلَيْمَانَ يَقُولُ سَمِعْتُ الشَّافِعِيَّ رَحِمَهُ اللهُ يَقُولُ لَا يَحِلُّ لِأَحَدٍ أَنْ يَكْتَنِيَ بِأَبِي الْقَاسِمِ كَانَ اسْمُهُ مُحَمَّدًا أَوْ غَيْرَهُ قَالَ الْفَقِيهُ رَحِمَهُ اللهُ وَرُوِّينَا مَعْنَى هَذَا عَنْ طَاوُسٍ الْيَمَانِيِّ رَحِمَهُ اللهُ
English Translation
Abu Abdullah al-Hafiz informed us: I heard Abu al-Abbas Muhammad ibn Ya'qub say: I heard al-Rabi' ibn Sulayman say: I heard al-Shafi'i (may Allah have mercy on him) say: 'It is not permissible for anyone to use the kunya Abu al-Qasim, whether his name is Muhammad or otherwise.' The jurist (may Allah have mercy on him) said: We narrated the same meaning from Tawus al-Yamani (may Allah have mercy on him).