Sahih al-Bukhari 2852
Sahih al-Bukhari · Book 56: Fighting for the Cause of Allah (Jihaad) · Jihad is to be carried on whether the Muslim ruler is good or bad
Narrated `Urwa Al-Bariqi:
حَدَّثَنَا أَبُو نُعَيْمٍ ، حَدَّثَنَا زَكَرِيَّاءُ ، عَنْ عَامِرٍ ، حَدَّثَنَا عُرْوَةُ الْبَارِقِيُّ ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " الْخَيْلُ مَعْقُودٌ فِي نَوَاصِيهَا الْخَيْرُ إِلَى يَوْمِ الْقِيَامَةِ الأَجْرُ وَالْمَغْنَمُ " .
The Prophet (ﷺ) said, "Good will remain (as a permanent quality) in the foreheads of horses (for Jihad) till the Day of Resurrection, for they bring about either a reward (in the Hereafter) or (war) booty (in this world)."