The Book of Prayer - Travellers
وَحَدَّثَنَا أَبُو الرَّبِيعِ الزَّهْرَانِيُّ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ عَمْرِو بْنِ دِينَارٍ، عَنْ جَابِرِ بْنِ زَيْدٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى بِالْمَدِينَةِ سَبْعًا وَثَمَانِيًا الظُّهْرَ وَالْعَصْرَ وَالْمَغْرِبَ وَالْعِشَاءَ .Ibn 'Abbas reported that the Messenger of Allah (ﷺ) observed in Medina seven (rak'ahs) and eight (rak'ahs), i. e. (be combined) the noon and afternoon prayers (eight rak'ahs) and the sunset and 'Isha' prayers (seven rak'ahs)
From Sahih Muslim, whose reports the scholars accept as authentic.