‘By Allah, indeed it is a grave matter that the likes of you, a descendent of two Imāms of guidance – meaning Umar and Ibn Umar – is asked about a matter and you have no knowledge of it’. So [al-Qāsim] said: ‘By Allah, more grave than that according to Allah, and to whoever reflects about Allah, is to speak without knowledge or to report on authority of one who is not trustworthy’. [Ibn Uyaynah] said that Abū Aqīl Yahyā bin al-Mutawakkil witnessed them both when they said that.  

أَخْبَرُونِي عَنْ أَبِي عَقِيلٍ صَاحِبِ بُهَيَّةَ أَنَّ أَبْنَاءً لِعَبْدِ اللَّهِ بْنِ عُمَرَ سَأَلُوهُ عَنْ شَىْءٍ لَمْ يَكُنْ عِنْدَهُ فِيهِ عِلْمٌ فَقَالَ لَهُ يَحْيَى بْنُ سَعِيدٍ وَاللَّهِ إِنِّي لأُعْظِمُ أَنْ يَكُونَ مِثْلُكَ وَأَنْتَ ابْنُ إِمَامَىِ الْهُدَى يَعْنِي عُمَرَ وَابْنَ عُمَرَ تُسْأَلُ عَنْ أَمْرٍ لَيْسَ عِنْدَكَ فِيهِ عِلْمٌ فَقَالَ أَعْظَمُ مِنْ ذَلِكَ وَاللَّهِ عِنْدَ اللَّهِ وَعِنْدَ مَنْ عَقَلَ عَنِ اللَّهِ أَنْ أَقُولَ بِغَيْرِ عِلْمٍ أَوْ أُخْبِرَ عَنْ غَيْرِ ثِقَةٍ قَالَ وَشَهِدَهُمَا أَبُو عَقِيلٍ يَحْيَى بْنُ الْمُتَوَكِّلِ حِينَ قَالاَ ذَلِكَ