Narrator:Umar ibn al-Khattāb
وَعَنْ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ كَانَ إِذَا بَعَثَ عُمَّالَهُ شَرَطَ عَلَيْهِمْ: أَنْ لَا تَرْكَبُوا بِرْذَوْنًا وَلَا تَأْكُلُوا نَقِيًّا وَلَا تَلْبَسُوا رَقِيقًا وَلَا تُغْلِقُوا أَبْوَابَكُمْ دُونَ حَوَائِجِ النَّاسِ فَإِنْ فَعَلْتُمْ شَيْئًا مِنْ ذَلِكَ فَقَدْ حَلَّتْ بِكُمُ الْعُقُوبَةُ ثُمَّ يُشَيِّعُهُمْ. رَوَاهُمَا الْبَيْهَقِيُّ فِي شُعَبِ الْإِيمَانِ
When 'Umar b. al-Khattab sent out his governors he laid on them the condition that they should not ride a horse not of Arabian breed,* or eat white bread, or wear fine clothing, or shut their gates against the needs of the people, telling them that if they did any of these things punishment would befall them. Then he would accompany them some distance. Baihaqi transmitted in Shuab al iman. * Birdhaun. This word is used of a horse of poor breed, a horse not of Arab breed, or more specifically a Turkish horse. It is suggested that the reason for the wording is to warn governors against riding horses, this being a sign of pride. Prohibiting a breed considered second-rate makes it obvious that to ride horses of the best Arab breed would be even a greater sign of pride.
Cited in Mishkat al-Masabih (No. 3730).