Not graded
Sunan ad-Darimi 421
أَخْبَرَنَا عَفَّانُ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ عَنْ ابْنِ عَوْنٍ عَنْ مُحَمَّدٍ قَالَ إِنَّ هَذَا الْعِلْمَ دِينٌ فَلْيَنْظُرْ الرَّجُلُ عَمَّنْ يَأْخُذُ دِينَهُ
This hadith has no English translation yet: the Arabic text, the reference and the grade are shown here.
Reported by Ad-Darimi (No. 421).