Sunan Abi Dawud 1305
سنن أبي داود#1305Sahihحَدَّثَنَا أَحْمَدُ بْنُ مُحَمَّدٍ، - يَعْنِي الْمَرْوَزِيَّ - حَدَّثَنَا وَكِيعٌ، عَنْ مِسْعَرٍ، عَنْ سِمَاكٍ الْحَنَفِيِّ، عَنِ ابْنِ عَبَّاسٍ، قَالَ لَمَّا نَزَلَتْ أَوَّلُ الْمُزَّمِّلِ كَانُوا يَقُومُونَ نَحْوًا مِنْ قِيَامِهِمْ فِي شَهْرِ رَمَضَانَ حَتَّى نَزَلَ آخِرُهَا وَكَانَ بَيْنَ أَوَّلِهَا وَآخِرِهَا سَنَةٌ .
Narrated Ibn 'Abbas:When the opening verses of Surah Al-muzammil was revealed, the Companions would pray as long as they would pray during Ramadan until its last verses were revealed. The period between the revelation of its opening and the last verses was one year
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: 5:56