صحيح ابن خزيمه
Sahih Ibn Khuzaymah
جماع أبواب الفريضة فى السفرChapters on Prayers while Traveling
(392) بَابُ نُزُولِ الرَّاكِبِ لِصَلَاةِ الْفَرِيضَةِ فِي السَّفَرِ،392 Chapter: The Traveler Dismounting to Pray the Obligatory Prayer While Traveling.
Hadith Q976
فَرْقًا بَيْنَ الْفَرِيضَةِ وَالتَّطَوُّعِ فِي غَيْرِ الْمُسَابَقَةِ وَالْتِحَامِ الْقِتَالِ وَمُطَارَدَةِ الْعَدُوِّ
Due to the difference between obligatory and voluntary prayers, if at that time he is not engaged in a confrontation, fierce battle with the enemy, or attacking the enemy (because in these situations, it is permissible to perform even the obligatory prayer on a mount).
