In a long narration al-Fadhl bin Shazan gives reasons for different rulings in Islam. Ali bin Muhammad bin Qutaybah al-Nesaboori asks al-Fadl bin Shazan after hearing the reasonings from him,

حَدَّثَنا عَبْد الواحِدِ بْنِ مُحَمَّدِ بْنِ عَبْدُوسٍ النِيْسابُوري العَطَّار رَضِىَ اللهُ عَنْهُ قالَ: حَدَّثَنا عَلِىِّ بْنِ‏قُتَيْبَةَ النِيْسابُوريُّ قالَ قُلْتُ لِلْفَضْلِ بْنِ شَاذَانَ لَمَّا سَمِعْتُ مِنْهُ هَذِهِ الْعِلَلَ أَخْبِرْنِي عَنْ هَذِهِ الْعِلَلِ أَذَكَرْتَهَا عَنِ الاسْتِنْبَاطِ وَالاسْتِخْرَاجِ وَهِيَ مِنْ نَتَائِجِ الْعَقْلِ أَوْ هِيَ مِمَّا سَمِعْتَهُ وَرَوَيْتَهُ فَقَالَ لِي مَا كُنْتُ لاعْلَمَ مُرَادَ اللَّهِ عَزَّ وَجَلَّ بِمَا فَرَضَ وَلا مُرَادَ رَسُولِ اللَّهِ‏ صَلَّى اللهُ عَلَيْهِ وَآلِهِ بِمَا شَرَعَ وَسَنَّ وَلا عِلَلَ ذَلِكَ مِنْ ذَاتِ نَفْسِي بَلْ سَمِعْتُهَا مِنْ مَوْلايَ أَبِي الْحَسَنِ عَلِيِّ بْنِ مُوسَى الرِّضَا عَلَيْهِ السَّلامُ الْمَرَّةَ بَعْدَ الْمَرَّةِ وَالشَّيْ‏ءَ بَعْدَ الشَّيْ‏ءِ فَجَمَعْتُهَا

"Inform me of these reasonings that you have mentioned, these are deductions (Istinbaat) and extractions (Istikhraaj) and these are results on the mind or are they what you have heard and narrated?"

al-Fadl bin Shazan said, "I did not know of the intention of Allah (عز وجل) regarding what he obligated, nor do I know the intention of Messenger of Allah (صلى الله عليه وأله) regarding the laws (Shariah) He made and Sunnah He established, nor do I know the reasons for those from my own-self, but I have heard them from my Master Abu al-Hasan Ali bin Musa Rida (عليه السلام) at different times one after the other, then I have collected them."

[Source: Uyoon al-Akhar al-Rida, Vol. 1, Pg. 127]