Mishkat al-Masabih 19 Jihad كتاب الجهاد 95

وَعَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ قَالَ: أُهْدِيَتْ رَسُول الله صلى الله عَلَيْهِ وَسلم بغلةٌ فركِبَهَا فَقَالَ عَلِيٌّ: لَوْ حَمَلْنَا الْحَمِيرَ عَلَى الْخَيْلِ فَكَانَتْ لَنَا مِثْلُ هَذِهِ؟ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّمَا يَفْعَلُ ذَلِكَ الَّذِينَ لَا يعلمُونَ» . رَوَاهُ أَبُو دَاوُد وَالنَّسَائِيّ

‘Ali told that God’s Messenger was presented with a she-mule which he rode, so ‘Ali said, “If we made asses cover mares we would have animals of this type,” to which God’s Messenger replied, “Only those who do not know do that.” Abu Dawud and Nasa’i transmitted it.