Sunan an-Nasai Book 21, Hadith 1978

أَخْبَرَنَا مُحَمَّدُ بْنُ رَافِعٍ، قَالَ أَنْبَأَنَا عَبْدُ الرَّزَّاقِ، قَالَ أَنْبَأَنَا ابْنُ جُرَيْجٍ، قَالَ سَمِعْتُ نَافِعًا، يَزْعُمُ أَنَّ ابْنَ عُمَرَ، صَلَّى عَلَى تِسْعِ جَنَائِزَ جَمِيعًا فَجَعَلَ الرِّجَالَ يَلُونَ الإِمَامَ وَالنِّسَاءَ يَلِينَ الْقِبْلَةَ فَصَفَّهُنَّ صَفًّا وَاحِدًا وَوُضِعَتْ جَنَازَةُ أُمِّ كُلْثُومٍ بِنْتِ عَلِيٍّ امْرَأَةِ عُمَرَ بْنِ الْخَطَّابِ وَابْنٍ لَهَا يُقَالُ لَهُ زَيْدٌ وُضِعَا جَمِيعًا وَالإِمَامُ يَوْمَئِذٍ سَعِيدُ بْنُ الْعَاصِ وَفِي النَّاسِ ابْنُ عُمَرَ وَأَبُو هُرَيْرَةَ وَأَبُو سَعِيدٍ وَأَبُو قَتَادَةَ فَوُضِعَ الْغُلاَمُ مِمَّا يَلِي الإِمَامَ فَقَالَ رَجُلٌ فَأَنْكَرْتُ ذَلِكَ فَنَظَرْتُ إِلَى ابْنِ عَبَّاسٍ وَأَبِي هُرَيْرَةَ وَأَبِي سَعِيدٍ وَأَبِي قَتَادَةَ فَقُلْتُ مَا هَذَا قَالُوا هِيَ السُّنَّةُ ‏.‏

Ibn Juraij said:"I heard Naji, claim that Ibn 'Umar offered the funeral prayer for nine together. He put the men closer to the Imam and the women closer to the Qiblah, and he placed them (the women) in one row. And the body of Umm Kulthum bint 'Ali the wife of 'Umar bin Al-Khattab, and a son of hers called Zaid were placed together. The Imam that day was Saeed bin Al-As and among the people were Ibn 'Umar, Abu Hurairah, Abu Saeed and Abu Qatadah. The boy was placed closer to the Imam. A man said something objecting to that, so I looked at Ibn 'Abbas, Abu Hurairah, Abu Saeed and Abu Qatadah and said: 'What is this?' They said: 'It is the Sunnah