Hadith 2:39
Mu'awiya said that the Prophet forbade the discussion of thorny questions. Abu Dawud transmitted it.
وَعَنْ مُعَاوِيَةَ قَالَ: إِنَّ النَّبِيَ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنِ الْأُغْلُوطَاتِ. رَوَاهُ أَبُو دَاوُد
Original Reference: Mishkat al-Masabih 243