كتاب الصلاة
2  
The Book of Prayer
Abu Nu'aim has in his Mustakhraj of Muslim, "While on a journey, if the sun declined he (ﷺ) used to pray Zuhr and 'Asr together and then continue his journey."
وَلِأَبِي نُعَيْمٍ فِي "مُسْتَخْرَجِ مُسْلِمٍ": { كَانَ إِذَا كَانَ فِي سَفَرٍ, فَزَالَتْ اَلشَّمْسُ صَلَّى اَلظُّهْرَ وَالْعَصْرَ جَمِيعًا, ثُمَّ اِرْتَحَلَ }

Sunnah.com reference : Book 2, Hadith 352
English translation : Book 2, Hadith 0
Arabic reference : Book 2, Hadith 438