Sunnah.com reference : Book 8, Hadith 125English translation : Book 8, Hadith 1082Arabic reference : Book 8, Hadith 1071
Narrated Ibn 'Abbas (RA):
In the time of Allah's Messenger (ﷺ), Abu Bakr (RA) and the first two years of the caliphate of 'Umar (RA), the three pronouncements of divorce were regarded as one divorce. So 'Umar said, "People have made haste in an affair which they are required to take slowly. What if we execute it on them." So, he executed it on them.

[Reported by Muslim].
وَعَنِ اِبْنِ عَبَّاسٍ ‏- رَضِيَ اَللَّهُ عَنْهُمَا‏- قَالَ : { كَانَ اَلطَّلَاقُ عَلَى عَهْدِ رَسُولِ اَللَّهِ ‏- صلى الله عليه وسلم ‏-وَأَبِي بَكْرٍ , وَسَنَتَيْنِ مِنْ خِلَافَةِ عُمَرَ , طَلَاقُ اَلثَّلَاثِ وَاحِدَةٌ , فَقَالَ عُمَرُ بْنُ اَلْخَطَّابِ : إِنَّ اَلنَّاسَ قَدْ اِسْتَعْجَلُوا فِي أَمْرٍ كَانَتْ لَهُمْ فِيهِ أَنَاةٌ , فَلَوْ أَمْضَيْنَاهُ عَلَيْهِمْ ? فَأَمْضَاهُ عَلَيْهِمْ }  .‏ رَوَاهُ مُسْلِمٌ  1‏ .‏‏1 ‏- صحيح .‏ رواه مسلم ( 1472 )‏.‏