Sunan an-Nasa'i 602
سنن النسائي#602Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الْعَزِيزِ بْنِ أَبِي رِزْمَةَ، - وَاسْمُهُ غَزْوَانُ - قَالَ حَدَّثَنَا الْفَضْلُ بْنُ مُوسَى، عَنِ الأَعْمَشِ، عَنْ حَبِيبِ بْنِ أَبِي ثَابِتٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُصَلِّي بِالْمَدِينَةِ يَجْمَعُ بَيْنَ الصَّلاَتَيْنِ بَيْنَ الظُّهْرِ وَالْعَصْرِ وَالْمَغْرِبِ وَالْعِشَاءِ مِنْ غَيْرِ خَوْفٍ وَلاَ مَطَرٍ . قِيلَ لَهُ لِمَ قَالَ لِئَلاَّ يَكُونَ عَلَى أُمَّتِهِ حَرَجٌ .
It was narrated from Ibn 'Abbas that the Prophet (ﷺ) used to pray in Al-Madinah combining two prayer. Joining Zuhr and 'Asr, and Maghrib and 'Isha', when there was no fear nor rain. It was said to him:"Why?" He said: "So that there would not be any hardship on his Ummah
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 6:109