Sunan an-Nasa'i 3406

أَخْبَرَنَا أَبُو دَاوُدَ، سُلَيْمَانُ بْنُ سَيْفٍ قَالَ حَدَّثَنَا أَبُو عَاصِمٍ، عَنِ ابْنِ جُرَيْجٍ، عَنِ ابْنِ طَاوُسٍ، عَنْ أَبِيهِ، أَنَّ أَبَا الصَّهْبَاءِ، جَاءَ إِلَى ابْنِ عَبَّاسٍ فَقَالَ يَا ابْنَ عَبَّاسٍ أَلَمْ تَعْلَمْ أَنَّ الثَّلاَثَ، كَانَتْ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَبِي بَكْرٍ وَصَدْرًا مِنْ خِلاَفَةِ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا تُرَدُّ إِلَى الْوَاحِدَةِ قَالَ نَعَمْ ‏.‏

It was narrated from Ibn Tawus, from his father, that Abu As-Sahba' came to Ibn 'Abbas and said:"O Ibn 'Abbas! Did you not know that the threefold divorce during the time of the Messenger of Allah and Abu Bakr, and during the early part of 'Umar's Caliphate, used to be counted as one divorce?" He said: "Yes

Reference

Sunan an-Nasa'i 3406

In-book

Book 27, Hadith 18