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.

حَدَّثَنَا 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 ‏.‏