Not graded
Bulugh al-Maram 438c
وَلِأَبِي نُعَيْمٍ فِي
"مُسْتَخْرَجِ مُسْلِمٍ"
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."
Cited in Bulugh al-Maram (No. 438c).