Authentic
graded by Al-Albani
Mishkat al-Masabih 634
عَن ابْن مَسْعُود وَسمرَة بن جُنْدُب قَالَا: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «صَلَاةُ الْوُسْطَى صَلَاةُ الْعَصْرِ» . رَوَاهُ التِّرْمِذِيُّ
Ibn Mas'ud and Samura b. Jundub reported God's Messenger as saying, "The middle prayer is the afternoon prayer.” Tirmidhi transmitted it.
Cited in Mishkat al-Masabih (No. 634).