Sahih al-Bukhari 3302
Narrated `Uqba bin `Umar and Abu Mas`ud:
Allah's Messenger (ﷺ) pointed with his hand towards Yemen and said, "(True) Belief is Yemenite, towards here (i.e. 
the Yemenite, had True Belief and embraced Islam readily). Certainly sternness and mercilessness are the 
qualities of those who are loud and at the base of the tails  of camels, where the two 
horns of Satan will appear. Such qualities belong to the tribes of Rabi`a and Mudar."
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ إِسْمَاعِيلَ، قَالَ حَدَّثَنِي قَيْسٌ، عَنْ عُقْبَةَ بْنِ عَمْرٍو أَبِي مَسْعُودٍ، قَالَ أَشَارَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِيَدِهِ نَحْوَ الْيَمَنِ فَقَالَ ‏
"‏ الإِيمَانُ يَمَانٍ هَا هُنَا، أَلاَ إِنَّ الْقَسْوَةَ وَغِلَظَ الْقُلُوبِ فِي الْفَدَّادِينَ عِنْدَ أُصُولِ أَذْنَابِ الإِبِلِ، حَيْثُ يَطْلُعُ قَرْنَا الشَّيْطَانِ فِي رَبِيعَةَ وَمُضَرَ ‏"‏‏.‏