Narrated Ibn `Abbas:

I intended to ask `Umar about those two ladies who back each other against 'Allah's Messenger (ﷺ) . For one year I was seeking the opportunity to ask this question, but in vain, until once when I accompanied him for Hajj. While we were in Zahran, `Umar went to answer the call of nature and told me to follow him with some water for ablution. So I followed him with a container of water and started pouring water for him. I found it a good opportunity to ask him, so I said, "O chief of the Believers! Who were those two ladies who had backed each other (against the Prophet)?" Before I could complete my question, he replied, "They were `Aisha and Hafsa."

حَدَّثَنَا الْحُمَيْدِيُّ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، قَالَ سَمِعْتُ عُبَيْدَ بْنَ حُنَيْنٍ، يَقُولُ سَمِعْتُ ابْنَ عَبَّاسٍ، يَقُولُ أَرَدْتُ أَنْ أَسْأَلَ، عُمَرَ عَنِ الْمَرْأَتَيْنِ اللَّتَيْنِ، تَظَاهَرَتَا عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَمَكُثْتُ سَنَةً فَلَمْ أَجِدْ لَهُ مَوْضِعًا، حَتَّى خَرَجْتُ مَعَهُ حَاجًّا، فَلَمَّا كُنَّا بِظَهْرَانَ ذَهَبَ عُمَرُ لِحَاجَتِهِ فَقَالَ أَدْرِكْنِي بِالْوَضُوءِ فَأَدْرَكْتُهُ بِالإِدَاوَةِ، فَجَعَلْتُ أَسْكُبُ عَلَيْهِ وَرَأَيْتُ مَوْضِعًا فَقُلْتُ يَا أَمِيرَ الْمُؤْمِنِينَ مَنِ الْمَرْأَتَانِ اللَّتَانِ تَظَاهَرَتَا قَالَ ابْنُ عَبَّاسٍ فَمَا أَتْمَمْتُ كَلاَمِي حَتَّى قَالَ عَائِشَةُ وَحَفْصَةُ‏.‏
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 437
Arabic reference : Book 65, Hadith 4915